x-axis denotes time in minutes and y-axis denotes distance (in blocks) away from the house.
He left home at zero time, so he started at origin (0,0).
He went to store which is at 6 blocks away from home, he walked at a speed of 3 blocks every 4 minutes. So he walked for 8 minutes to cover 6 blocks distance from home. It means the store is at (8,6). So its graph would be a straight line going from (0,0) to (8,6).
Then he stopped and went into the store for 5 minutes. He stayed at store from point (8,6) to (13,6). Its graph would be horizontal line from (8,6) to (13,6).
Then he went back to home at speed of 2 blocks every 3 minutes, so he walked for 9 minutes to cover 6 blocks distance back to home. It means he returned home at (22,0). So its graph would be a straight line going from (13,6) to (22,0).
The graph is attached herewith the solution.