Wolfgang and Heinrich worked as electricians at $14 and $12 per hour respectively. One month Wolfgang worked 10 hours more than Heinrich. If their total income for the month was $3520, how many hours did each work during the month?

Let us say that:

x = hours worked by Wolfgang

y = hours worked by Heinrich

So that:

x = y + 10

14 x + 12 y = 3520

By combining the two equations:

14 (y + 10) + 12 y = 3520

14 y + 140 + 12 y = 3520

26 y = 3380

y = 130 hours

x = y + 10 = 140 hours

So Wolfgang worked 140 hours while Heinrich worked 130 hours.