In the previous step we found the following just before using a direct substitution to find the velocity at a particular time.

To find the velocity at general time t = a, we need to first simplify as much as possible.

v(a) = limₕ→₀ (18(a + h) - 1.86(a + h²) - (18a - 1.86a²)/h
= limₕ→₀ (18a + 18h - 1.86(a² + (_____) ah + h²) - 18a + 1.86a²)/h
= limₕ→₀ 18a + 18h - 1.86a² + (_____) ah + 1.86h²) - 18a + 1.86a²)/h
= limₕ→₀ 18h - (_____) ah + 1.86h²)/h
= limₕ→₀ 18 - (_____) a + 1.86h