The number 72 should replace the question mark.
Step-by-step explanation:
Step 1:
First, we need to determine how the values inside the triangles were attained in terms of the outer values.
We get that summing the bottom values on the triangle and multiplying it with the value on top equals the value in the triangle.
For triangle 1,
For triangle 2,
For triangle 3,
Step 2:
By using the same method for the fourth triangle we have;
For triangle 4:
So the question mark equals 72.