Let, p, q, r and s be positive natural numbers having three exact factors including 1 and the number itself. If q > p and both are two-digit numbers, and r > s and both are one-digit numbers, then the value of the expression p - q - 1r - s is:

Answer: Option C

q > p and r > s
q > p > r > s
All number have three prime factor
One digit → s, r
s → 2         2² = 4
r → 3         3² = 9
Two digit → p, q
p → 5     5² = 25
q → 7     7² = 49
$$\begin{array}{rl}& \frac{p-q-1}{r-s}=\frac{25-49-1}{9-4}=\frac{-25}{5}=-5\\ & -5=-4-1=-s-1\end{array}$$