# How do you solve 21=5n-2(n-3)?

$n = 5$
Use the distributive property, which states that $a \left(b + c\right) = a b + a c$.
$2 \left(n - 3\right) = 2 n - 6$
$21 = 5 n - \left(2 n - 6\right) \implies 3 n + 6 = 21 \implies 3 n = 15 \implies n = 5$