□ input data

Assuming :
The horizontal and vertical reaction forces at point A are RHA and RVA, respectively.
The vertical reaction force at point B is RVB.
The horizontal direction is + to the right (→), and the vertical direction is + upward (↑).

The horizontal reaction force RHA acts only at point A, and since the sum is zero,

∑H = RHA - P*H = 0

Since the sum of moments at point B is zero,

∑MB = RVA*L - P*H*H/2 = 0

Since the sum of forces in the vertical direction is zero,

∑V = RVA + RVB = 0