Use the formula for the total accomplishment, as written below.
A=nrt
Where A is the total accomplishment by n number of workers at time t, r is the rate of work done.
As given,
\frac{2}{5}=1\times r\times5\left(8\right),
r=\frac{1}{100}
Now, find the number of hours Silvana has to knit per day to finish the blanket on time.
1-\frac{2}{5}=1\times\frac{1}{100}\times\left(9-5\right)h,
h=15
So, Silvana has to knit 15 hours per day to finish the blanket on time.