Question 4 : witch numbers in the box are multiple of 3

 6 and 12 are the only multiples of 3

To check if it is a multiple of 3:

add the digits and then divide by 3

if there is no remainder it is a multiple of 3

1+2 = 3

3/3 =1 no remainder it is a multiple of 3

20 = 2+0 = 2

2/3 = 0 remainder 2   not a multiple of 3

what’s the question?

using pemdas, (order of operations) you'll see the answer is 24.