24m-16-13=60+15m+28
24m-15m=60+28+16+13
9m=117
m=117:9
m=13
(a-b)*(a+b)=a^2-b^2. (a-5)*(a+5)=a^2-25. (a-√b)*(a+√b)=a^2-b
(√7-√x)*(√7+√x)=7-x. (√6-√5)*(√6+√5)=6-5=1