The answer to all of these problems

1) area of a cicular pool
area of a circle=πr^2   d=2.5 then r=2.5/2
A=3.14 *(2.5/2)^2
A=4.906m^2 A=4.9m^2

2) arae of a coin 
(if i read it right d=15mm?)
A=πr^2   d=15 then r=15/2
A=3.14*(15/2)^2 =176.6mm^2

Rest all are same problems u try to solve it