For the circuit shown,

$R_1=10k$

$R_2=47k$

$R_3=15k$

$R_f=150k$

$v_{i1}=0\mathrm{.}7V$

$v_{i2}=-5V$

$v_{i3}=-1V$

What is the output voltage $v_0?$

$13\mathrm{.}5$ V

$-12V$

$15\mathrm{.}5$ V

$-15\mathrm{.}5V$