well, he has "x", which oddly enough is 100%, and we also know that 42 is 35% of that, so
[tex]\begin{array}{ccll} amount&\%\\ \cline{1-2} x & 100\\ 42& 35 \end{array} \implies \cfrac{x}{42}=\cfrac{100}{35}\implies \cfrac{x}{42}=\cfrac{20}{7} \\\\\\ 7x=840\implies x=\cfrac{840}{7}\implies x=120[/tex]
