The forth and seveth terms of an A. P are 3 and 36. Find the A.P and its fifteenth term

Answer 1

a+3d = 3
a+6d=36

subtract them:
3d = 33
d = 11

then a+33 = 3
a = -30

AP is -30 -19 -8 3 14 ...
term(15) = a+14d = -30+14(11) = 124