How many meatballs does raul still need to make if he already has 25 and needs a total of 32 for sunday’s dinner? b represents the number of meatballs raul needs.

We need to examine what are the known factors in the word problem. b represents the number we need to find out. 32 is the goal and 25 is how many Raul currently has, so we construct the equation by finding the difference between the end goal and the current result and to find the difference we subtract.
Goal - Current Result = b
32 - 25 = b 
b = 7, the difference between the goal and the current result