We are asked to find the value of angle $p$ in the given diagram. The angles $40^\circ$, $85^\circ$ and $p$ form a straight line.

1. Problem Description

We are asked to find the value of angle $p$ in the given diagram. The angles $40^\circ$, $85^\circ$ and $p$ form a straight line.

2. Solution Steps

A straight line has an angle of $180^\circ$. Therefore, the sum of the given angles must be equal to $180^\circ$.

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

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

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

$p = 55^\circ$

3. Final Answer

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