first 10 hours = $8 × 10 = $80
to save at least $270, 90% of earnings, means that 90%*x = 270
.9x = 270
.9x/.9 = 270/.9
x = 300
So has to make at least $300, which - $80
= $220
220/$10/hr = 22 hours
He must work at least 22 hours at the new rate the rest of the week to save at least $270