Tom ate 1/4 of a pizza. he divided the leftover pizza into pieces each equal to 1/12 of the original pizza. after he gave some friends 1 piece each, 1/6th

Tom ate 1/4 pizza, so that left him with 3/4 pizza. 

Now that 3/4 is divided into 1/12 , so now he got 3/4  : 1/12
 = 9 slices of 1/12 pizzas , or 9/12 of the original pizzas

Now it remained 1/6 or 2/12 of the original pizzas.

which mean, the amount of friends that got pizza are : 9 - 2 = 7 friends

hope this helps