How do i calculate these and express the answers in significant digits?

Question

2.865 x 10^4m x 1.47 x 10^3
8.071 cm^2/ 4.216
1.142 x 10^-8 mm^2 / 8.5 x 10^-4 mm

i tried the first one and got 4212. but i don't know if it's right

Answer 1

I don't understand the questions since some have units and others don't.
For first one, I have
2.865E4 x 1.47E3 = 4.21155E7. The first number has 4 s.f. and second has 3 s.f. The rule in multiplying is that the final answer may have no more s.f. than any of the numbers multiplied. Therefore, you are allowed 3 s.f. in the answer so you would round to 4.21E7. I don't know what unit that 1.47E3 has.If it isn't m that may complicate the problem a little.