Resposta :
✔OLÁ!!!
A) 4 , 8 , 12 ........ AN
A2 - A1
8 - 4 = 4
An = A1 + ( N - 1 ) . R
An = 4 + ( 8 - 1 ) . 4
An = 4 + 7 . 4
An = 4 + 28
An = 32
B) - 20 , - 5 , 0 , 5
An = A1 + ( N - 1 ) . R
An = - 20 + ( 8 - 1 ) . 5
An = - 20 + 7 . 5
An = - 20 + 35
An = 15