Answer
t=12
Work Step by Step
If it takes them 6 days to complete the house the let that be $\frac{1}{6}$. If it takes Clarissa 5 days less than Shawna to complete the house then Let that be ($\frac{1}{t}$-$\frac{1}{5}$). Then let Shawna be ($\frac{1}{t}$+$\frac{1}{5}$).
($\frac{1}{t}$-$\frac{1}{5}$)+ ($\frac{1}{t}$+$\frac{1}{5}$)=$\frac{1}{6}$
[$\frac{2}{t}$=$\frac{1}{6}$]*[$\frac{6t}{1}$]
(2*6)=t
12=t