Three Is The Magic Number
De la Soul sang, “Three is the magic number” and indeed that couldn’t be truer here. The answer is of course 3! Did you figure it out? After various tries of division, multiplication, addition and subtraction, we are sure you nailed it.

The left side of the triangle uses subtract, e.g. 6-2 = 4, which when multiplied by the width 4 equals 8, the middle number. The right side of the triangle has no mathematical instruction so don’t be confused by that. Apply this to all triangles and you will reach 3 for the last triangle. See, that wasn’t so bad.