The formula of a midpoint between two points:

We have:

Substitute:

Answer: 
It is 19. Hope this helps!!
if they’re separate triangles then x would be 8 considering the triangle further away has a patterned measurement
Probability that first student prefers mechanical pen = 0.30
P(first student does not and second student does) = 0.70 * 0.3 = 0.21)
P( selecting 2 or fweer) = 0.30+ 0.21) = 0.51 or 51%