Answer
The gravitational acceleration is
$$g_Z=1.77\text{ m/s}^2.$$
Work Step by Step
The horizontal distance is covered with the constant velocity (we suppose that the gravitational acceleration is strictly vertical) so we have
$$d_h=v_ht\Rightarrow t=\frac{d_h}{v_h}.$$
Now, the vertical distance is covered with uniform gravitational gravitational acceleration $g_Z$ so we have
$$d_v=\frac{1}{2}g_Z t^2=\frac{1}{2}g_Z\frac{d_h^2}{v_h^2}=\frac{g_Zd_h^2}{2v_h^2}$$
which yields
$$g_Z=\frac{2d_vv_h^2}{d_h^2}=\frac{2\cdot1.40\text{ m}\cdot 6.95^2(\text{ m/s})^2}{8.75^2 \text{ m}^2}=1.77\text{ m/s}^2.$$
