a+3(5a+8)=72
Carry out the multiplication of the parentheses.
3(5a+8) = 15a + 24
Plug that back into the equation.
a+ 15a+24 = 72.
Can be simplified as
16a+24 = 72
Simplified further by dividing (by 4, in this case)
4a + 6 = 18.
Now, we can subtract 6 from both sides.
4a = 12.
Divide by 4 to isolate a.
a = 3.