[rmarkdown] LaTeX {exam} template with integrated R

cover.tex

\begin{coverpages}
\begin{center}
% provide instructions and details
\fbox{\fbox{\parbox{5.5in}{\centering
		Answer the questions in the spaces provided on the question sheets. \linebreak
		If you run out of room for an answer, continue on the back of the page.}}}
\end{center}

\vspace{1in}
\makebox[0.9\textwidth]{Name:\enspace\hrulefill}

\vspace{0.5in}

\makebox[0.9\textwidth]{Student Number:\enspace\hrulefill}

\vspace{1in}

% add grade table
\begin{center}
\gradetable[h]
\end{center}

\end{coverpages}

% header and footer
\thispagestyle{headandfoot}
\firstpageheader{}{Page \thepage\ of \numpages}{}
\runningheader{}{Page \thepage\ of \numpages}{}
\firstpagefooter{}{}{}
\runningfooter{}{}{}
\runningheadrule
\firstpageheadrule

preamble.tex

% define questions and solutions and parts
\newcommand{\BQ}{\begin{questions}}
\newcommand{\EQ}{\end{questions}}

\newcommand{\BS}{\begin{solution}}
\newcommand{\ES}{\end{solution}}

\newcommand{\BP}{\begin{parts}}
\newcommand{\EP}{\end{parts}}

% pandoc does not understand parts. Must use {} in markdown
\renewcommand{\part}[1][]{\oldpart[1]{}}

skeleton.Rmd

---
title: "Class Code"
subtitle: "Exam Name"
date: "`r format(Sys.Date(), '%d-%m-%Y')`"
documentclass: exam
classoption: [answers, addpoints] # comment to hide answers
fontsize: 12pt
output:
  pdf_document:
    highlight: NULL
    includes:
      before_body: cover.tex
      in_header: preamble.tex
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE, fig.height = 4, fig.width = 4, fig.align = 'center')
```
\BQ

# Pressure 

\question[5] Define pressure

\BS

 * Under
 * Pressure
 
\ES
\vspace{\stretch{5}}
\newpage

# Trees 
\question Looks at the graph below

```{r trees}
plot(Height ~ Girth, trees)
```

\BP
  \part[2]{} What is the predictor variable?
  \BS
    Girth
  \ES
  \vspace{\stretch{2}}
  \part[3]{} What is the dependent variable?
  \BS
    Height
  \ES
  \vspace{\stretch{3}}
\EP

\EQ