Tunde and Shola can do the work in 18 days.
Both will do the work in \(\frac{1}{18}\) days.
But Tunde can do the whole work in x days; Hence he does \(\frac{1}{x}\) of the work in 1 day.
Shola does the work in (x + 15) days; hence, he does \(\frac{1}{x + 15}\) of the work in 1 day.
\(\frac{1}{x} + \frac{1}{x + 15} = \frac{1}{18}\)
\(\frac{2x + 15}{x^{2} + 15x} = \frac{1}{18}\)
\(x^{2} + 15x = 36x + 270\)
\(x^{2} + 15x - 36x - 270 = 0\)
\(x^{2} - 21x - 270 = 0\)