How many are there?

$ab-2a=24$

$a(b-2a)=24$ now b is independent of a, So number of solution of the $x\times y$ $=$ $24$ will also be of that of question . $24$ $=$ $2^{3}$ $3^{1}$ Which is $(3 + 1)$ $(1+1)$ =8

ab -2a = 24. Factors of 24 are 1, 2, 3, 4, 6, 8, 12, 24.....eight.
a can take these $\color{#D61F06}{eight}$ values and b corresponding values.