The horizontal grid lines are 10 °C apart, so 45 °C corresponds to a vertical position halfway between the 4th grid line and the one marked 50.
The graph intersects that position at the 2nd vertical grid line. The vertical grid lines are 3 minutes apart, so the 2nd grid line represents 6 minutes.
If Peter conducted the experiment from its start until the temperature reached 45 °C, he conducted it over a period of 0 to 6 minutes, inclusive:
