Which is the best estimate of the solution to this system of equations?

A:linear function for both :

beach: y=-2x+100 (x=0, y=100)

dunes=5x+20 ( when x=0, y=20 (year1995)

B: after almost 11 years: it will be year 2006  and 2007 (after 11.429 years)

C: when the two rates of erosion are equal at the rate of 77 and almost 11 years

-2x+100=5x+20

-2x-5x=-100+20

-7x=-80

-80/-7=x

x=11.429

y=77.143