Question 1142597
x, unknown amount of L or 5 % acetic acid
H, concentration of higher, 50 % acetic acid
L, concentration of lower, 5% acetic acid
T, target concentration, 10 %
V, amount of the H % acid, known given


{{{Lx+HV=T*(x+V)}}}

-

{{{Lx+HV=Tx+TV}}}

{{{Lx-Tx=TV-HV}}}

{{{Tx-Lx=TV-HV}}}

{{{(T-L)x=TV-HV}}}

{{{highlight(x=(TV-HV)/(T-L))}}}
Solved for x.  Substitute the known, given values and evaluate x.