The student did not divide x by 72 to isolate x completely.
After you have isolated a variable, if there is still a number attached to it, you must take the appropriate measures to remove it.
We'll use four examples here to display this.
x^2 = 100
for this, we must find the square root √ of both sides in order to isolate x.
x = 10
√x = 5
To find what x equals, we must square both sides to remove the √.
x = 25
5x = 10
To remove 5 from the variable, we must divide both sides by 5.
x = 2
x/5 = 4
To remove the /5 from x, we must multiply both sides by 5.
x = 20
Let me know if you have any questions!
