Answer
$=-5a^{11}b$
Work Step by Step
Group factors with the same base: $$\frac{25a^{13}b^{4}}{-5a^{2}b^{3}}$$
$$=(\frac{25}{-5})(\frac{a^{13}}{a^{2}})(\frac{b^{4}}{b^{3}})$$
When dividing factors with the same non-zero base, subtract the exponent of the denominator from the exponent of the numerator:
$$=-5a^{(13-2)}b^{(4-3)}$$
$$=-5a^{11}b$$
