PR=18mm
AB=7mm
All lengths of triangle PRQ are twice the lengths of ACB
For this case we have by definition, that the equation of a line in the slope-intersection form is given by:

Where:
m: It's the slope
b: It is the cutoff point with the y axis
We need two points through which the line passes to find the slope:

We found the slope:

So, the equation is of the form:

We substitute a point to find "b":

Finally, the equation is:

Answer:
Option D
Answer:
C. 
Step-by-step explanation:
Given the two equations:

To find:
The correct option when value of y is substituted to 2nd equation using the 1st equation.
Solution:
First of all, let us learn about the substitution method.
Substitution method is the method to provide solutions to two variables when we have two equations and two variables.
In substitution method, we find the value of one variable in terms of the other variable and put this value in the other equation.
Now, the other equation becomes only single variable and then we solve for the variable's value.
Here, we have two equations and value of one varible is:

Let us put value of y in 2nd equation:

So, the correct answer is option C. 