Try factoring the polynomials, and see if one of the factors is the divisor. So for the first one,
x^2 + 7x + 10 = (x+2) (x + 5)
so, x+2 is one of the factors, so the answer is x+5.
For the 2nd one, note that x^-25= (x+5)(x-5)
and 2x-10= 2(x-5).