What is the change in internal energy $(E)$ of a system when it gains $35\mathrm{.}0$ J thermal energy and does $15\mathrm{.}0$ J of work?

$+20\mathrm{.}0$ J

$+50\mathrm{.}0$ J

$-50\mathrm{.}0J$

$-20\mathrm{.}0J$