Answer
20 mph of the wind
Work Step by Step
distance = rate * time
with wind: 400 = (230+x)*t
against wind: 336 = (230-x)*t
$400=(230+x)*t$
$400/(230+x)=(230+x)*t/(230+x)$
$400/(230+x)=t$
$336 = (230-x)*t$
$336/(230-x) = (230-x)*t/(230-x)$
$336/(230-x) =t$
$400/(230+x) = 336/(230-x)$
$336*(230+x) = 400*(230-x)$
$77280 +336x = 92000 - 400x$
$736x = 14720$
$736x/736 = 14720/736$
$x=20$