-16x = - 352 step equations

For the rule of 78, for a 12-month period, the last term in the sequence is 12 and the series sums to 78. for an 10 month period, the last term is and the series sum is . for a 15 month period, the last term is and the series sum is . for a 20 month period, the last term is and the series sum is

You receive 15% of the profit from a car wash how much money do you receive from a profit of 300

I’m stuck on this equation, anyone got the answer?