the three numbers are 49,56 and 63.
It is not differentiable at x=1 since the slope of the tangent line as x -> 1 from the right is 1 while the slope of the tangent line as x->1 from the left is -1
Y=x+3 because when x=0 y=3
Midpoint formula
mid of (x1,y1) and (x2,y2) is

so
(22,15)=

therefor
22=

and
15=

slv each
22=

times both sides by 2
44=18+x1
minus 18 both sides
26=x1
15=

times both sides by 2
30=6+y1
minus 6
24=y1
the other point is (26,24)
Answer: d/dx (f(x)) = 2x + 5
Ok done. Thank to me :>