Help on Physics homework? Converting

How do i convert 50ps to Gs??

Convert 200MW to mW??

50 ps = 50*10^-12 s = (50*10^-12)*{(10^-9)*(10^9)} s = (50*10^-12)*{(10^-9)}{*(10^9)} s
(50*10^-12)*{(10^-9)}G s = 5*10^-20 Gs

200MW = 200*10^6 W = 200*(10^6)*{(10^3)*(10^-3) W = 200*(10^6)*{(10^3)*{(10^-3) W}
= 200*(10^6)*{(10^3) mW = 2.0*10^11 mW

50 ps = 50*10^-12 s = 50*10^-21*10^21*10^-12 s = 50*10^-21 Gs
all you have to do is juggle powers of ten.