r^2+8r=48
First bring the 48 to the other side of the equation
r^2+8r-48=0
Now you can use the quadratic formula.
x=-b+-sqrt(b^2-(4ac))
¯¯¯¯¯¯¯2a¯¯¯¯¯¯¯¯¯
So...
a=1
b=8
c=-48
Now just plug the numbers into the quadratic equation and get your two answers.
The answers are: x=-12 and x=4
Feel free to ask if you need any more help. :-)