To calculate horizontal acceleration when only displacement and time are given, you need to have information about the initial velocity. With that information, you can use the following equation:
a = (2 * Δx) / (t^2),
where: a is the horizontal acceleration, Δx is the displacement, t is the time.
Please note that this equation assumes that the initial velocity is zero. If the initial velocity is not zero, you need to consider it in your calculations. In that case, you can use the following equation:
a = (2 * Δx - 2 * v₀ * t) / (t^2),
where: v₀ is the initial velocity.
Remember to use consistent units throughout your calculations, such as meters for displacement and seconds for time.