Hello!
Let's write this as a system of equations.
L= 5/2s
12= 2L-2s
Let's plug our L value into the second equation and solve for s.
12= 2(5/2s)-2s
12 5s-2s
12=3s
s=4
Now let's plug s into the first equation.
L=5/2(4)
L=10
Therefore, our numbers are 10 and 4.
I hope this helps!