$-12r-48=-10\left( r-3 \right)$
Distribute $-10$ through the parentheses$-12r-48=-10r+30$
Move the variable to the left-hand side and change its sign$-12r-48+10r=30$
Move the constant to the right-hand side and change its sign$-12r+10r=30+48$
Collect like terms$-2r=30+48$
Add the numbers$-2r=78$
Divide both sides of the equation by $-2$$r=-39$