We are given
total cost is y thousand dollars
number of engines produced is x
We can select any two points
so, we can select those two points as
(0,2) and (20,7)
Let's assume


(A)
Since, we have to find equation of line y
so, we can use slope intercept form of line
that is

where
m is slope
b is y-intercept
step-1:Finding slope (m)
we can use formula





now, we can plug these values


step-2: Finding y-intercept (b)
we know that
y-intercept is value of y when x=0
we are given (0,2)
so,

step-3: Finding equation of line
we can find equation of line
..........Answer
(B)
we are given
number of engines =50
so, we can plug x=50 and find y


so, y=14.5 thousand dollars
y=14.5*1000=$14500
The total cost of producing 50 engines is $14500..........Answer