Answer:
she took 13 classes that were worth 3 credits
Step-by-step explanation:
well we know that some of the classes are worth 3 and some are worth 4 and that all of these together = 59 so your first equation would be
3x+4y=59
x would be the number of classes worth 3 credits and y would be the number of classes worth 4 credits.
then it says the total number of classes that they took was 18 so we know that
x + y =18.
you want to solve for the number of 3 credit classes so lets go ahead and get rid of the y values. SO you need you multiply the x+y equation by 4
4x+4y=72
then subtract 4x+4y=72 from 3x+4y=59 to get
-x = -13
and then x is a negative so you need to divide -1 from both sides and you get that she took 13 classes that were worth 3 credits.
