maximums, displacements, velocity real easy stuff

here is a question for you maths legends out there

Damien is standing in a yard, when Sophie runs away from her

At any time t = [0,10], her displacement is given by S1= -0.5t (squared) + 12t, and his displacement is given by S2 = 0.7t (squared)

b) what time is the distance between them a maximum

c) assume damo cant see her if she gets 35m away. Is she safe?

d) what is sophie;s velocity at any time t? what is damiens velocity at any time t?

e) what would you expect their velocities to be in comparison with each other at the exact time when the distance between them is at a maximum?

f) at what time does he catch her? explain why there is 2 answers.

THANKS HEAPS - ANY HELP WOULD BE JUST GREAT .. GOOD ON YA