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?

80x+60x=560

140x=560

X=4

4*2=8 so Marissa earned $40 a week for 8 weeks

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.