Answer is 23
Logic
The sum of equilateral triangles are equal, hence, if triangle A has
13+20+34= 67
Then, Triangle B should equal 67
16+28+?= 67
44+? = 67
?= 67-44
?= 23
Hence, the missing number to make the sum of triangle B 67 is 23
Logic
The sum of equilateral triangles are equal, hence, if triangle A has
13+20+34= 67
Then, Triangle B should equal 67
16+28+?= 67
44+? = 67
?= 67-44
?= 23
Hence, the missing number to make the sum of triangle B 67 is 23