a) V=-5000t+141200
b)after 13 years the bulldozer´s value will be 76200
Step-by-step explanation
Step 1
set the equation:
as the bulldozer depreciates linearly, we can use a linear function to represent the situatio.
a linear function has the form

so
a) let t represent s the time
let V represents the value of the bulldozer
so, we have 2 coordinates
I)One company buys a new bulldozer for $141200

ii) Its salvage value at the end of 25 years is $16200,so

b) now, we have 2 points, we can find the slope using the formula
the slope of line is given by:

then, let

replace to find the slope

so, the slope of the line is -5000
c) finally,get the function of the line, use the slope-point equation

so,let

replace and solve for y

finally, rewrite the functino using the original variable

so,
a) V=-5000t+141200
Step 2
now, the value after 13 years,
to know that,let t = 13 and evaluate

therefor, after 13 years the bulldozer´s value will be 76200
I hope this helps you