There are 2 brands of fertilizers containing nitrogen and water. Gentle green is 5% nitrogen and sun saver is 15% nitrogen. We need to combine two types of solutions in order to make 100 litres of 12% nitrogen. How much of each brand should be used?

0.05x + 0.15x = 0.05 + 0.15 ( 100 + 0.12 )

Is that equation correct ?