p^-4 x -5p
In properties of exponents, if the exponent is negative then you move the variable with the negative exponent to the denominators place and it changes to positive and the numerator becomes 1.
p^-4=1/(p^4)
Also, if no exponent is present it is understood to be 1.
Keeping this in mind,
p^-4 x -5p
1/(p^4) x -5p^1 substituted p^-4 by 1/p^4 and added ^1 to -5p
-5p^1/p^4 multiplied-5p^1 to 1
-5/p^3 simplified