How would I solve this?

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

The value of x in this system of equations is 1. 3x + y = 9 y = –4x + 10 substitute the value of y in the first equation: combine like terms: apply the subtraction property of equality: apply the division property of equality: 3x + (–4x + 10) = 9 –x + 10 = 9 –x = –1 x = 1 what is the value of y?

Ithink i know it but i want to be sure so can you me out ?