To make this easy let covert everything using a LCD.
The LCD of 1/4 1/12 and 1/6 is 12. This becomes...
Tom ate 3/12 of the pizza.
Leftover pizza = 9/12.
Slices were 1/12.
X friends got pizza.
Remaining pizza is 2/12.
if each friend got 1 piece(1/12)....
9/12(Leftovers) - 2/12(remaining) = 7/12
So 7 friends got pizza.
Find a common denominator for 2,4,8. Which is 8. Change the fractions to new ones.
1) 19 4/8= 156/8 Then add the second. 2) 7 5/8= 61/8 one and the third
3) 5 6/8= 46/8 one. Which is
15/8. Then, subtract your answer and the first one. You get 141. Simplify. 17 5/8
To figure this out, you do 63 - 20 which is 43. I hope this helps!
by dy/dx, we'll be assuming that "y" is encapsulating a function, a function in terms of "x".

Answer:
Hey there!
40+12(27)+18
40+324+18
364+18
382
Let me know if this helps :)