Question

If 3x + 9y = 21 , find the value of 4(x + 3y)

Answer 1

25

Explanation:

The method that should be used is substitution:

Do this by taking 3x+9y=21 and transforming it to be
`y=-(1)/(2) x+(7)/(3)`

Once you have this, substitute the value of y that we just found into 3x+9y=21 to find the value of x:
`3x+9(-(1)/(2) +(7)/(3) ) =21`

Solve for x. You should get 1.5

Once you have this, Plug in 1.5 for the value of x into the y= equation that we found in the beginning:
`y=-(1)/(2) (1.5)+(7)/(3)`

Solve for y. You should get 1.583 (19/12)

Plug in the values of x and y that we found into the last equation to find its value: 4(1.5+3(1.583))