Answer:
First Solution: 8.5mL
Second Solution: 42.5 mL
Step-by-step explanation:
Let us call x the number of mL of the first solution and y the number of mL of the second solution.
Now, from the fact that the final solution is 51 mL, we know that

Furthermore, from the fact that the final solution 40% carbonated water, meaning there are in total

of carbonated water in the love potion.
Now, the first solution contributes 15/100 * x mL of carbonated water in the solution whereas the second solution contributes 45/100 * y mL. Since all 20.4 mL of carbonated water in the solution is coming from solution 1 and 2, then it must be that


Thus we have two equations and two unknowns

We solve the above system by elimination.
First multiplying the second equation by 0.15 gives

which simplifies to give

Subtracting the first equation from the second gives

Finally, dividing both sides by 0.30 gives

With the value of y in hand, we now put it into x+ y = 51 and solve to x to get

subtracting 42.5 from both sides gives

Hence, to conclude the needed amounts of the solution are:
First Solution: 8.5mL
Second Solution: 42.5 mL