question says she can work a maximum of 60 hours per week.
the w-axis is for TOTAL WEEKLY earnings, which includes the 40 hours she worked before
all of the graphs have their horizontal axes labeled as "number of hours worked over 40"
so you HAVE to stop at 20 hours worked over 40 hours, otherwise she will work over 60.
so we can ignore choices C and B because they go 40 hours worked over 40 hours, which would have a total of 80 hours of work
the "w"-intercept here is $250, no problems there (since u get $250 per week for working 40 hours... these graphs are only concerned with hrs after 40 so by default she already has 250 for these graphs)
if she has $10 per hour, then the slope is $10/hour
(slope is rise/run. if we run for 1 hour, we have to rise $10, hence slope being $10/1 hour)
the equation for this is
w = 10h + 250
so after working for 40 hrs, if she works for 20 hours more, we plug in h=20
w = 10(20)+ 250
= 200 + 250
= 450
so there should be point (20, 450) on the graph
choice A