Answer
15 hours
Work Step by Step
Briley takes 24 hours, Briley’s son takes 40 hours
$(1/24 + 1/40)*x=1$
$(1/24*5/5 + 1/40*3/3)*x=1$
$(5/120 + 3/120)*x = 1$
$8/120*x=1$
$8/120*x*120/8=1*120/8$
$x=120/8$
$x=60/4$
$x=15$
15 hours
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