Statement #1:
Since there are 30 total pizzas then the amount of pizzas with 12 slices is 60% of 30 which is 18. Then you can multiply 18 by 12 to get the amount of slices in the large pizzas with 12 slices:
18 × 12 = 216
-----------------------------------------------------------------------------------------------------------------
60% of the pizzas have 12 slices each. In total, there are 216 slices in these pizzas.
Statement #2
There are 12 remaining pizzas which means that 12 × 10 = 120 is the amount of slices in total of the smaller pizzas.
-----------------------------------------------------------------------------------------------------------------
40% of the pizzas have 10 slices each. In total, there are 120 slices in these pizzas.
Statement #3
To get the total amount of pizzas you simply add both of the previous solutions:
216 + 120 = 336
-----------------------------------------------------------------------------------------------
Altogether, there is a total of 336 slices of pizza.