有無人識得做呢題數??好緊急!!

You have to be familiar with linear equation.

(a) The linear equation has the form y = mx + b
where m is the slope of the line and b is the y-intercept.

YEAR               SALES
2004(0)           $12.5 millions
2010(6)           $23.6 millions

You let x = 0 for year 2004, so x = 6 for year 2010
The x-coordinate is given by (Year – 2004), 2010-2004 = 6
Now let y represent the sales

The two points on x-y graph are (x1, y1) and (x2, y2)
They are (0, 12.5) and (6, 23.6)
It is assumed that the projected sales is approximated by a linear function.
X2
Slope of the line m = (y2 – y1)/(x2 – x1)
m = (23.6 – 12.5)/(6-0) = 11.1/6 = 1.85
b = 12.5 (y-intercept is value of y when x = 0)

The equation is y = 1.85x + 12.5


(b) year 2015 is equivalent to x = 11 (2015 -2004 = 11)
y = 1.85x + 12.5
substitute x = 11 into equation
y = 1.85(11) + 12.5 = 17.38 + 12.5 = 29.88

Sales in year 2015 is $32.85 millions


(c) When y = 40, what is x?
y = 1.85x + 12.5
40 = 1.85x + 12.5
1.85x = 40 – 12.5 = 27.5
x = 27.5/1.85 = 14.86 = 15
That is the year 2019 (2004 + 15 = 2019)

It is expected in year 2019, the sales will reach $40 millions.