P=3L-3W solve for L (literal equation)

P=3L-3W

Move - 3W to the other side. Sign changes to + 3W

P+3W=3L-3W+3W

P+3W=3L

Divide both sides by 3 to get L by itself

P/3+3W/3=3L/3

Cross out 3 and 3, divide by 3 and then becomes 1*1*W=W

Cross out 3 and 3, divide by 3 and then becomes 1*1*L=L

P/3+W=L

Answer:

L=P/3+W