Explanation:
if I understand the typing correctly, the question is to multiply
5p²q with -4p³q⁴
I will continue with that assumption :
5p²q × -4p³q⁴ = -5p²q4p³q⁴ = -5×4p²qp³q⁴ =
= -20p²qp³q⁴ = -20p²p³qq⁴ =
= -20×p^(2+3)×q^(1+4) = -20p⁵q⁵
the multiplication of multiplications allows us through the commutative law to simply "connect" both into one long sequence of multiplications.
and inside that sequence of multiplications we can move things around and then combine elements (like exponents of the same base term - remember, multiplying with exponents means adding the exponents).