A company offers two pricing plans for internet service. Plan A is represented by the line shown, where $C$ is the cost in dollars and $G$ is the data used in gigabytes. The line for Plan A passes through the points $(0,20)$ and $(10,50)$. Plan B charges a flat fee of $40plus$2 per gigabyte. For how many gigabytes of data is the cost of Plan A equal to the cost of Plan B?