A number exceeds its four-sevenths by 18. Find the number.

Let the required number be x.

Four-sevenths of the number = $\dfrac{4}{7}x$

According to the given condition we have:

$\phantom{=} x - \dfrac{4}{7}x = 18 \\[1em] \Rightarrow \dfrac{7x - 4x}{7} = 18 \\[1em] \Rightarrow \dfrac{3x}{7} = 18 \\[1em] \Rightarrow 3x = 18 \times 7 \\[1em] \Rightarrow 3x = 126 \\[1em] \Rightarrow x = \dfrac{126}{3} \\[1em] \Rightarrow x = 42$

Hence, the required number is 42.