First, draw a schematic representation of that situation:
The shortest distance between the starting point (Linus's house) and the endpoint (Charlie's house) is a straight line. Since a right triangle is formed with the sides of length 7 blocks and 3 blocks, we can use the Pyhtagorean Theorem to find the length of the hypotenuse:
Therefore, the shortest distance between those two points would be 7.6 blocks.