Answer
See the answer below.
Work Step by Step
$n_{cH,Reacted}=x, [cH]_{Equil}=(0.045-x)/V$
$n_{cP,Formed}=x, [cP]_{Equil}=x/V$
$K=[cP]/[cH]\rightarrow 0.12=x/(0.045-x)$
$x=0.0048\ mol$
At equilibrium: $[cH]=(0.045-0.0048)/2.8=0.014\ M, [cP]=0.0048/2.8=0.0017\ M$
