Question 201400
As  a  linear  relationship, it  follows  the  form,  y=mx +b.
.
In  this  case,,,R=mt +b,,,with  points (0,46.4),,and (70,45)
.
m= (y2-y1) / (x2-x1) = - (46.4 -45) /(1990 - 1920) = -1.4 / 70 = -.02
.
R = (-.02)t +b,,,,,@(0,46.4),,,46.4 = 0 +b,,,b=46.4
.
Base  eqn  ,,,,R = -.02t +46.4
.
@ 1990, t=1990-1920=70,,,R=-.02(70) +46.4 = 45,,,,,good  check
.
@ 2003, t=2003-1920=83,,,R=-.02(83)+46.4 = 44.74
.
@ 2006, t=2006-1920=86,,,R=-.02(86)+46.4 = 44.68
.
Have  a  great  day