As you know that sum of complementary angles equal 90°
so,
7x + 11x = 90
18x = 90
x = 90/18
x =5
so,
option A is the correct one.
For this case we have the following equation:

From here, we must substitute ordered pairs of the form:
(x, y)
If the ordered pair satisfies the equation, then it belongs to the line.
We have then:
For (8, 5):
We substitute the following values:

We observe that the equation is not satisfied and therefore, this point does not belong to the line.
Since one of the points does not belong to the line, then the equation is not a good model.
Answer:
It is not a good model. One of the points does not belong to the line.
Well, it all depends on how big the wall is so that way, you can find out how much of the wall they can cover per hour or per minute.