Question

you have to multiple 3.14 time the diameter
3.14*15
47.1
and then add 1
= 47.2

Answer 1

You have to multiple 3.14 time the diameter 
3.14*15
47.1
and then add 1
= 48.1 (Its 1 not .1)

Answer 2

is 48.1, because you need to add 1 to de 47