Plots not showing up in R html document - r

Question

I've written some simple code to plot some data, but for some reason I can't get it to print out on the html document when I knit it?
library(datasets)
library(ggplot2)
ggplot(ChickWeight, aes(x = Time, y = weight)) + geom_point()
I expect to see an image in the output, but instead, I just see the html code for one...
'''r
library(datasets)
library(ggplot2)
ggplot(ChickWeight, aes(x = Time, y = weight)) + geom_point()
'''
<img src="hw5_files/figure-html/unnamed-chunk-3-1.png" width="672" />
Is there any reason why this would be happening? I'm using Ubuntu 18.04 and R 3.4.4
Edit:
My entire markdown file for this looks like this:
---
title: DS Homework
author: Aaron
date: 4/10/2020
output: html_document
---
1. Question 1:
a. Some part a
b. Some part b
'''{r}
library(datasets)
library(ggplot2)
ggplot(ChickWeight, aes(x = Time, y = weight)) + geom_point()
'''
2. Question 2:

Answer 1

ggplot works well in "interactive" mode however when you are sourcing your code you need to explicitly call print(). Thus either
library(datasets)
library(ggplot2)
print(ggplot(ChickWeight, aes(x = Time, y = weight)) + geom_point())
or
library(datasets)
library(ggplot2)
p <- ggplot(ChickWeight, aes(x = Time, y = weight)) + geom_point()
print(p)
Should work
Hope it helps

Answer 2

I've since figured out that in fact, it was actually, because I was indenting the code blocks, unindenting the code blocks fixed the issue
1. Question 1:
a. Some part a
b. Some part b
'''{r}
library(datasets)
library(ggplot2)
ggplot(ChickWeight, aes(x = Time, y = weight)) + geom_point()
'''
2. Question 2:
to
1. Question 1:
a. Some part a
b. Some part b
'''{r}
library(datasets)
library(ggplot2)
ggplot(ChickWeight, aes(x = Time, y = weight)) + geom_point()
'''
2. Question 2:

Answer 3

put print() before the ggplot or any other plotting line
e.g
from
surface3d(wt1, hp1,pred, alpha=.2)
to
print(surface3d(wt1, hp1,pred, alpha=.2))
Alternatively you can these in the code chunk if you are using rgl library
options(rgl.useNULL = TRUE)
setupKnitr(autoprint=TRUE)
E.g.
\\```{r}
library(rgl)
options(rgl.useNULL = TRUE)
setupKnitr(autoprint=TRUE)
\\```