Mermaid, harp and Math

Mermaid is play melody graph of the function y = f (x) and y = g (x) to the accompaniment of the sound of the waves. At this point, sum of all real root of irrational equation ?

1) 15               2) Not 15

Since , root of irrational equation is -1, 7, 10. Sum of all real root is -1+7+10=16

So answer is No. 2) Not 15