Paper weight

How could you use this graph to work out the weight of a single sheet of paper?
Age
11 to 14
Challenge level
filled star empty star empty star
Exploring and noticing Working systematically Conjecturing and generalising Visualising and representing Reasoning, convincing and proving
Being curious Being resourceful Being resilient Being collaborative

Problem

The graph shows how the weight of a letter (including the envelope) varies with the number of sheets of paper used.

Paper Weight


What is the weight of a single sheet of paper?