Deduce the missing factor

a) [[$ 5 \cdot $]] [[$ = 75 $]]

b) [[$ \cdot 3^2 = 63 $]]

c) [[$ 2 \cdot 5^3 \cdot $]] [[$ = 2\:250 $]]

d) [[$ \cdot 6 \cdot 11 = 198 $]]