Answer:
h=84
Explanation:
You need to set up two equations. The first will be math + history = 240, or m + h = 240. and than you have to h = m - 72 and after that you have to use the second equation to replace the "h" in the first equation: m + m - 72 = 240. and than do 2m - 72 = 240 and solve it. and add 72 to both sides 2m=312 than divide both sides by 2 which will be m = 156 which than you do 156+ h and that will give you 240. than subtract 156 from both sides and your Answer would be here=84.