20 points need asap question in picture below

For this case we have the following solution.
 x = gallons of water to be added
 For the 10% solution we have:
 0.1 * 8 = 0.8
 Then, for 5% we have:
 (0.8 / x + 8) = 0.05
 Rewriting:
 (0.8 / x + 8) = (5/100)
 
 An equation can be used to find x, the humber of gallons of water he should add is:
 (0.8 / x + 8) = (5/100)