Answer
Paula made 8 free throws.
Work Step by Step
Let $m$ be the number of free throws made by Maria.
The number made by Paula is $2m$.
$m+2m=12$ $\longrightarrow$combine like terms
$3m=12$ $\longrightarrow$multiplication property
$3m\div3=12\div3$ $\longrightarrow$divide
$m=4$
$2m=2\times4=8$