HELP!! I dont understand this word problem!

Question

An investment is worth $3980 in 1994. By 1999 it has grown to $6380. Let y be the value of the investment in the year x, where x=0 represents 1994. Write a linear equation that relates the value of the investment, y, to the year x.

 

Could it be explained fully please?

Answer 1

x = number of years since 1994

y = value of investment in year x

 

Assuming that x and y are linearly related, 

(0, 3980) and (5, 6380) are two points on a line.

 

slope of line = (6380-3980)/(5-0)

                     = 2400/5 = 480

 

Use the point-slope form of the equation of a line:

 

    y - 3980 = 480(x - 0)

               

               y = 480x + 3980