The table shows the marks of 80 candidates in an exam…

Step 1. The running totals. $6, 20, 46, 68, 80$ at the limits $20, 40, 60, 80, 100$.

Step 2. The cut-off. $80 - 15 = 65$ candidates are below it. The height $65$ lies in the class $60$ to $80$, where the running total goes from $46$ to $68$. So the cut-off is $60 + \dfrac{65 - 46}{22} \times 20 = 60 + 17.27 = 77.27$ marks.

Step 3. Fewer than $50$. At $40$ marks the total is $20$. The class $40$ to $60$ has $26$ candidates, and $50$ is halfway through it, so we add $13$. The total is $20 + 13 = 33$.