Answer:
24
Step-by-step explanation:
Keep in mind that exterior angles are mentioned. So let's find the interior ones. Note that the interior and exterior angles are forming straight lines. So something plus 84 equals 180 degrees.
180-84=96
180-120=60
The sum of three angles of a triangle is 180 degrees. X is an angle. So we can form an equation to represent this. Then just solve for x!
96+60+x=180
156+x=180
x=24
Alright,
you will need to solve for each variable to find if they got the equation correctly or not..
Let's start with h
isolate h
(1/2)h = A/(b1+b2)
Now we need to get rid of 1/2 we may do so by multiplying both sides by 2
h = 2(A/(b1+b2))
And that's not how they did it for h so Option D doesn't apply
Let's see C
Also doesn't apply since they multiplied 2 only by A rather than A/h
Let's see B
Also not correct they made the same mistake as with option C
Let's see A
again same mistake
when multiplying both sides by 2
the 2 should be as following

I believe you should contact your instructor and explain that non of the options is right.
Y=x-7 this is because you subtracted the x to both sides. Since y is a negative, you divide by -1 causing the -x to turn positive and the positive seven to be negative seven.
Xy=30
x=6/11
6/11y=30
Divide by 6/11 on both sides
y=55