We are asked to find the size of angle $p$ in the given diagram. The angles around a point on a straight line add up to 180 degrees. In the diagram, the sum of the angles $40^{\circ}$, $85^{\circ}$ and $p$ forms a straight line.

1. Problem Description

We are asked to find the size of angle $p$ in the given diagram. The angles around a point on a straight line add up to 180 degrees. In the diagram, the sum of the angles $40^{\circ}$, $85^{\circ}$ and $p$ forms a straight line.

2. Solution Steps

The sum of angles on a straight line is $180^{\circ}$. Therefore,

$40^{\circ} + 85^{\circ} + p = 180^{\circ}$

Adding the known angles:

$125^{\circ} + p = 180^{\circ}$

Subtracting $125^{\circ}$ from both sides of the equation to isolate $p$:

$p = 180^{\circ} - 125^{\circ}$

$p = 55^{\circ}$

3. Final Answer

The size of angle $p$ is $55^{\circ}$.