Part (a)
Answer: 87
------------------
Work Shown:
v = u + a*t
v = 7 + 10*8 ... plug in the given values
v = 7 + 80
v = 87
==================================================
Part (b)
Answer: 10
------------------
Work Shown:
v = u + a*t
80 = 20 + 6*t .... plug in the given values
80-20 = 6t .... subtracting 20 from both sides
60 = 6t
6t = 60
t = 60/6 .... divide both sides by 6
t = 10