Apiano teacher charges $30 for a one hour lesson, and $50 for a two hour lesson. she works for 25 hours in one week, and earns $690. determine how many two hour lessons she gave.

Suppose the number of 2 hours lessons are x and 1 hour lessons are y; thus,
2x+y=25
50x+30y=690
to get the values of x and y we solve the quadratic equation given;
from the top equation:
y=25-2xi
substituting i in our second equation we get:
50x+30(25-2x)=690
50x+750-60x=690
-10x=-60
thus;
x=6
hence we conclude that the number of 2 hours classes are 6 hours