Question

$\left \{ {{ab=13} \atop {bc=9}} \right.$⇒a+b-c=? (a, b, c ∈ N)

Answer 1

{ab = 13,
{bc = 9;
a, b, c ∈ N ⇒ a = 13, b = 1, c = 9
a + b - c = 14 - 9 = 5