What’s 29.75 simplified?

John used linear combination to solve the system of equations shown. he did so by multiplying the first equation by -3 and the second equation by another number to eliminate the x-terms. what number did jonas multiply the second equation by? 4x-6y=23x+5y=11

Adam used 1072.4 gallons of water over the course of 7 days. how much water did adam use, on average, each day?

Having a hard time understanding this question (see attachment).