Answer
See below
Work Step by Step
Obtain $\frac{x+15}{x+17}=\frac{19}{20}$
Thus, we have: $x+15=19k\\x+17=20k$
Rewrite as: $x=19k-15\\x=20k-17$
Comparing $x$ from two equations:
$19k-15=20k-17\\k=2$
Find $x=19(2)-15=23$
Hence, the student should submit 23 consecutive assignments to raise her homework percentage up to 90%.
