14 and 15 are both choice B
The question is asking "how many substances has their mass recorded" to find the answer you would simply count how many substances (the dots above the graph) there are. After counting you will see that there are 13 which is the answer to your question.
Hope this helps! :)
Check the picture below
the triangles are similar, the angles are congruents then
so... just add them up, and divide by 2, or set them as rational
The answer would be 0.009321 (rounded)
complete would be 0.00932090545 which equals 7/751