Answer
$28.125$ minutes
Work Step by Step
Let both sarah and andy work together in $T$ minutes
(Fraction work done in a minute by Sarah)+ (Fraction work done in a minute by Andy)T=1
$\implies (\dfrac{1}{45}+\dfrac{1}{75})T=1$
$\implies (\dfrac{5+3}{225})T=1$
$8T=225$
or, $T=28.125$ minutes
