Answer:
a=57 b=62
Explanation:
u⁰=52
u¹=a
u²=b
u³=67
Use the explicit relation given by:
u(n)=u⁰+nd
where n is any term and d is the common difference.
u³=u⁰+3d
67=52+3d
3d=67-52
d=15/3
d=5
a=52+5=57
b=a+5=62
67=b+52=62+5=67 (just to make sure of the answer)