I need help solving for the height of a trapezoid and finding the correct final answer for a semi circle (a half circle).In area form

Here's what I have so far:
Trapezoid Formula: 1/2(b1+b2)h
My Answer:1/2(5+15)=10
(My bases are 5 and 15)
I need help solving for the height now.
I went with 7 but my teacher said I was wrong and I don't know how to solve for the height. Can someone please help correct me and teach me how to properly solve for the height.

Circle Formula: A=pi*r^2 /2
My answer:(3.14*7.5^2/2=174.624=175
My teacher said my Formula is correct but my final answer I wrong. I kinda figured that but I need help checking and seeing where I went wrong and how to properly fix it.

So can someone please help me? I'm finding the Area in these problems.

1 answer

If the area is 10, then
1/2(5+15)h = 10
1/2(20)h = 10
10h = 10
h = 1

If the radius is 7.5 (diameter=15) then
3.14*7.5^2/2
= 3.14*56.25/2
= 176.625/2
= 88.3125