The amount charged by the account in the first hour = $35
The amount charged by the accountant after first hour = $23
Total earnings of the accountant = $127
Let us assume that he worked for = x hours
then
35 + 23x = 127
23x = 127 - 35
23x = 92
x = 4
So from the above deduction we can conclude that the accountant worked for 4 hours. I hope the procedure is simple enough for you to understand.