Well you dont really have equations, you have expressions, you need to have an = sign for it to be an equation. But anyway, here goes.
1. (5t^4 - 10t^2)/(t^5 - 4t)
we cant really do much with this one, just factor a t from the top and bottom (did you learn factorization?).
so we get t(5t^3 - 10t)/t(t^4 - 4) = (5t^3 - 10t)/(t^4 - 4) since the t's cancel.
2. 15t^4/(10t^5 + 25t^3)
we can factor 5's out of the top and bottom, as well as t^3. so we get:
5t^3(3t)/5t^3(2t^2 + 5)
the 5t^3 cancels from the top and bottom leaving:
3t/(2t^2 + 5)
Are you sure there was no equal sign for these? If there is any step that ou dont understand, or if you dont understand how to factorize just tell me, i will explain simpler