Marissa earned $560 in the summer. she earned $40 each week for part of the summer and $60 each week for the rest. if she earned $40 each week twice as often as she earned $60, how many weeks did she earn $40?

She earned $40 each week twice as often as she earned $60.

Let us say she earned $60 for x weeks.

Therefore $40 was for  2x weeks.

Her total = $560.

40(2x) +  60(x) = 560
80x  + 60x = 560
140x = 560
x = 560 / 140 = 4
x = 4 weeks.
But $40  was for 2x  weeks.
 = 2*(4)  = 8.
$40  was for 8 weeks.