The probability of the first person ordering a meat topping would be 8/13 because 8 are meat out of the possible 13 toppings.
The probability of the second person ordering a different meat topping would be 7/12 because there are 7 other meat options out of now 12.
The probability of the third person ordering a different meat topping would be 6/11.
Multiply these fractions together. 8/13 x 7/12 x 6/11 = 28/143