This is because the constant of proportionality in each example given ($315 and 3 hours, $525 and 5 hours, $735 and 7 hours), is the same number with all of the values, which is 105. You can find this by dividing the dependant variable by the independent variable (In this case the money earned is dependant and the number of hours worked is independent).
you can do a ratio where you have 34 over 60 then cross multiply that ratio with x over 12 and 60x=408 and it equals 6.8 but I am assuming you have to round up.
