Answer:
12 sandwiches
Step-by-step explanation:
Make a proportion
He can make 6 sandwiches with 3 tomatoes, and x sandwiches with 6 tomatoes
6/3=x/6
Multiply both sides by 6 to isolate the variable, x
6*6/3=x/6*6
12=x
So, with 6 tomatoes, he can make 12 sandwiches
