Set up a system of equations.
x+y=46 where x=older and y=younger
y=10+1/3(x)
Change the form of the first equation to make it easy to combine.
y=46-x
y=10+1/3(x)
Now combine and solve.
46-x=10+1/3(x)
4/3(x)=36
x=27
The older brother is 27, so the younger brother has to be 19.
