The height (h) of a tree after (n) years is given by the equation h=4n+7. In how many years will the height be 39 feet?

2 Answers
Tony B
Jun 23, 2018

n=8

Explanation:

Set h=39=4n+7

Subtract 7 from both sides

color(green)(39=4n+7color(white)("dddd")->color(white)("dddd")39color(red)(-7) =4n+7color(red)(-7))

color(white)("dddddddddddddd")->color(white)("ddddd")32color(white)("d")=4ncolor(white)("d")+0

Divide both sides by 4

color(green)(32=4ncolor(white)("ddddddd")->color(white)("dddd")32/color(red)(4)=4/color(red)(4) n)

But 4/4 is the same as 1 and 1xxn=n giving:

32/4=n

(32-:4)/(4-:4) = 8/1=n=8

Written as per convention

n=8

Jim G.
Jun 23, 2018

8" years"

Explanation:

"we have to solve the equation for n"

4n+7=39

"subtract 7 from both sides"

4n=39-7=32

"divide both sides by 4"

(cancel(4) n)/cancel(4)=32/4rArrn=8

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