Left f(x) be a continuous function f(2)=10, f’(2)=-4 and f’’(x)=-6 for all X. Find the value of f(2.5)

since the slope is the derivative (-4), I plugged that in to y=mx+b and got 10=-4(2)+b, to solve for b and got 18=b. So my equation is y=-4x+18. I then solved for y, which is 8. So f(2.5)=8.....is that right?