Let
x----------> number of weeks
y----------> total money
we know that
Judy's saving equation can be modeled as follows
y=20+6x------------> equation 1
and
Ida's spending equation can be modeled as follows
y=172-4x----------> equation 2
to know when they will have the same amount
equation 1=equation 2
20+6x=172-4x------------> 6x+4x=172-20----------> 10x=152------> x=15.2
x=15.2 weeks
the answer is 15.2 weeks
