Answer
$2a(5a+6)$
Work Step by Step
First find the greatest common factor of $10a^2\ and\ 12a$. Find the prime factors of each.
$10a^2=\underline2 \times 5 \times \underline a\times a$
$12a= \underline2 \times2\times3 \times \underline a$
The greatest common factor is the product of the common factors (underlined above).
$2\times a=2a$
$10a^2+12a=2a(5a+6)$
