Answer
$c=6$
Work Step by Step
$3(5c+1)-12=13c+3$ $\longrightarrow$ distributive property
$15c+3-12=13c+3$ $\longrightarrow$ simplify
$15c-9=13c+3$ $\longrightarrow$addition property
$15c-9-13c+9=13c+3-13c+9$ $\longrightarrow$simplify
$2c=12$ $\longrightarrow$multiplication property
$2c\div2=12\div2$ $\longrightarrow$simplify
$c=6$