To solve the problem, we first determine the total distance that Joel biked in the first part of his trip:
- He biked 9 blocks East.
- He biked 12 blocks North.
The total distance biked away from the starting point is the sum of these distances: \[ 9 + 12 = 21 \text{ blocks} \]
Now, we need to find the most direct route back to the starting point. The position after biking 9 blocks East and 12 blocks North can be represented as a point with coordinates (9, 12).
To return to the starting point (0, 0), we need to travel:
- 9 blocks West (opposite of East)
- 12 blocks South (opposite of North)
The distance back is the same as the distance traveled out: \[ 9 + 12 = 21 \text{ blocks} \]
Now we total all the blocks biked (both out and back): \[ \text{Total distance} = 21 \text{ blocks (out)} + 21 \text{ blocks (back)} = 42 \text{ blocks} \]
Thus, the total number of blocks that Joel would ride altogether is: \[ \boxed{42} \]