Slope of y=1-2x is -2
Using point intercept form:
y-1=-2(x-3)
y-1=-2x+6
y=-2x+7
35 students would not know any of the three languages, because if 30 know French, 19 knew German, and 16 knew Russian, that must mean that 65 students know at least one of the three languages. So you subtract 65 from 100 and end up with 35
20/21 is the answer to your problem.
I think u forgot to put pic for we can see the triangle
