The graph shows the proportional relationship between the number of gems collected and the number of levels that have been completed in a video game.

Graph with x axis labeled game levels and y axis labeled gems collected. A line begins at 0 comma 0 and goes through points 6 comma 420 and 8 comma 560.

Determine the constant of proportionality for the relationship.
p = 70
p = 140
p equals 2 over 140
p = 0.0143