Answer
Please see the work below.
Work Step by Step
We can find the partial pressure of $N_2$ as:
$N_2=\frac{1}{6}\times 866mmHg=144.3mmHg$
We can find the partial pressure of $H_2$ as:
$H_2=\frac{3}{6}\times 866mmHg=433mmHg$
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