25 / 2 = 12.50

12.50 – 2 = 10.50, price of book

12.50 +2 = 14.50, price of cd

Check it… 14.50 + 10.50 = 25.00

First add like terms (the x’s) to get

2x + 4 = 25

now subtract 4 from each side

2x + 4 – 4 = 25 – 4 thus 2x = 21

now divide both sides by 2

2x / 2 = 21 / 2 thus x = 10.50

book = x = $10.50 cd = $10.50 + $4.00 = $14.50

CHECK $10.50 + $14.50 = $21.00

Formula: cost of cd + cost of book = 25 or

x + y = 25

But cost of cd is $4 greater than the cost of book, so x = y+4.

Substituting the value of x in the formula, we get

x+y = 25

y+4+y = 25

2y = 25 – 4

y = 21/2

y = 10.50

Therefore, the cost of the book is $10.50.

book = x

cd = book + $4 = x + $4

(x + $4) + x = $25

x + $4 + x = $25

2x + $4 = $25

2x = $25 – $4

x = ($25 – $4)/2 = $10.50

book = x = $10.50

book + (book + 4) = 25

book + book = 25 – 4

2 x book = 21

book = $10.50

book 10.50

14.50-cd