Y = mx + b
in this case m = 2 and b = 1 so
equation
y =2x + 1
hope this helps
diameter (d) = 2 · r
Circumference (C) = 2 π · r → C = π · d → d = 
Y=17400(1+0.025)^8 is your equation and with that you get $21200.21
Y =Mx + C
where M = gradient / slope
C = y intercept
comparing with y = 2x - 3
M = 2
C = -3