To find the area of a circle, you have to use the area formula:
r being your radius
A = 
Substitute 1 in for r
A = 
A = 
Hello!
7.5 * 4 is equal to 30
7 * 4 = 28
.5 * 4 = 2
28 + 2 = 30
I hope this helps, and have a nice day!
For 16 it's 8/10 for 17 it's 52/100 for 18 it's -92/100 for 19 it's -48/100 for 20 it's 86/100 for 21 it's 76/100