A line plot is a data display, along a number line, which shows frequency.
The frequency is indicated by a marker, like an X or a dot.
First, find the totals for each length.
There are 2
x's above
$11\frac{1}{2}$ feet. Multiply
$11\frac{1}{2}$ feet by 2.
$11\frac{1}{2}$ ft × $2$ = $\frac{23}{2}$ ft × $2$ = $\frac{46}{2}$ ft = $23$ ft
There are 4
x's above
$11\frac{5}{8}$ feet. Multiply
$11\frac{5}{8}$ feet by 4.
$11\frac{5}{8}$ ft × $4$ = $\frac{93}{8}$ ft × $4$ = $\frac{372}{8}$ ft = $46\frac{4}{8}$ ft = $46\frac{1}{2}$ ft
There are 3
x's above
$12\frac{1}{4}$ feet. Multiply
$12\frac{1}{4}$ feet by 3.
$12\frac{1}{4}$ ft × $3$ = $\frac{49}{4}$ ft × $3$ = $\frac{147}{4}$ ft = $36\frac{3}{4}$ ft
There are 2
x's above
$13\frac{1}{2}$ feet. Multiply
$13\frac{1}{2}$ feet by 2.
$13\frac{1}{2}$ ft × $2$ = $\frac{27}{2}$ ft × $2$ = $\frac{54}{2}$ ft = $27$ ft
Now, find the sum of all of the totals.
$23$ ft + $46\frac{1}{2}$ ft + $36\frac{3}{4}$ ft + $27$ ft 
= 
$23$ ft + $46$ ft + $\frac{1}{2}$ ft + $36$ ft + $\frac{3}{4}$ ft + $27$ ft 

= 
$132$ ft + $\frac{1}{2}$ ft + $\frac{3}{4}$ ft 

= 
$132$ ft + $\frac{2}{4}$ ft + $\frac{3}{4}$ ft 

= 
$132$ ft + $\frac{5}{4}$ ft 

= 
$132$ ft + $1\frac{1}{4}$ ft 

=  $133\frac{1}{4}$ ft 
So, if placed endtoend, the total length of all of the compact cars would be $133\frac{1}{4}$ feet.