A cookie recipe calls for 1 1/2 teaspoons of baking soda for each 2 cups of flour. How many teaspoons would be required for 7 cups of flour

1 1/2 : 2 = x : 7 

leads to 
1.5/2=x/7 
x=7*1.5/2=5.25 
5 1/4 teaspoons