we added 175 X 12. is that the correct method
Not exactly sure what you mean by added 175 X 2 since "X' is multiplication. It looks like did the correct math, however, I have included an equation below you need to understand the problem.
average mass of an item = (total mass) / number of items
So, the 175 grams is the average mass of one peach and your total number of peaches is 12. Put these into the equation and solve for total mass of the carton of peaches.
175 grams = (total mass) / 12
Total mass = 175 grams X 12 = 2100 grams.