## Algebra 1

Let both mark and lynn clean the office in $T$ hours together. (Fraction work done in a minute by mark)+ (Fraction work done in a minute by lynn)=1 $\implies (\dfrac{1}{30}+\dfrac{1}{40})T=1$ $\implies (\dfrac{4+3}{120})T=1$ $7T=120$ or, $T=17.142$ hours or, $T \approx 17$ minutes