I assume it is the diameter of the outer wheel they are asking for.
connect OD, which is the radius of the wagon to the outer edge of the wheel.
OYD is a right triangle. use the hypotenuse theorem:
OY²+YD²=OD²
7²+24²=OD²
OD=√625
OD=25
the radius is 25, the diameter is then 50.
Note: if it is the diameter of the inner circle they are asking for, I don't know.
