$\text{Percentage of passed students} = \frac{\text{Percentage of boys passed} \times \text{#boys}+ \text{Percentage of girls passed}\times\text{#girls}}{\text{Total number of students}}$
Taking total number of students as $x$ and from the given statements,
$80 = \frac{\text{Percentage of boys passed} \times \frac{4}{4+3}x + 90 \times \frac{3}{4+3}x}{x}$
$\implies80 \times 7 = 4 \times \text{Percentage of boys passed} + 3 \times 90 $
$\implies \text{Percentage of boys passed} = \frac{560-270}{4} = \frac{290}{4} = 72.5$
Correct Answer: B