20 weeks, earnings $(15 + 35), spending $300:
<span>20(15 + 35) - 300 = amount of money she has left
</span>
3x+10y=48
7x+4y=54
multiply the first equation by 2 and the 2nd equation by 5 to remove y
6x+20y=96
35x+20y=270
29x=174
x=6
substitute to any equation
7x+4y=54
42+4y=54
4y=12
y=3
the value of x is 6 and the value of y is 3