A + AB + AC + ABC = 21 (A = only like A, AB = only like A and B but not C, etc.)

You can express all the other given values in the same way, so you can get the following information

A + AB + AC + ABC = 21

B + AB + BC + ABC = 26

C + AC + BC + ABC = 29

AB + ABC = 14

AC + ABC = 12

BC + ABC = 14

ABC = 8

You need to know C.

C + AC + BC + ABC = 29

This is the only expression with C in, so you’ll obviously need to use this equation. You will also need some way to work out the values of AC, BC and ABC

AC + ABC = 12

BC + ABC = 14

ABC = 8

ABC = 8, so this can be substituted in whenever you see ABC

C + AC + BC + 8 = 29 // C + AC + BC = 21

AC + 8 = 12 // AC = 4

BC + 8 = 14 // BC = 6

You can now substitute in the values of AC and BC

C + 4 + 6 = 21

C = 11

11 people like only C

12 + 14 + 8 is 34 which is more than 29 meaning that there is some overlap making this question tricky. I arrived at 3 by including the 8 that liked all 3 in the earlier groups (this could be a flaw in my logic). Now for sure 12 + 14 = 26 and 29-26=3

Total 29 liked Product C.

12 people liked C & A

14 liked B & C

8 liked A, B and C

So the total people who like C along with other products is 34?? Doesnt make any sense bro!