Answer:
4 toothpicks, for the pattern part, you always need 3 more toothpicks to make another square
Step-by-step explanation:
To make 1 square use 4 toothpicks; to make 2 squares use 7 toothpicks; to make 3 squares use 10 toothpicks. For each new square you needs a further 3 toothpicks.
