Answer:
25
Step-by-step explanation:
The method that should be used is substitution:
Do this by taking 3x+9y=21 and transforming it to be [tex]y=-\frac{1}{2} x+\frac{7}{3}[/tex]
Once you have this, substitute the value of y that we just found into 3x+9y=21 to find the value of x: [tex]3x+9(-\frac{1}{2} +\frac{7}{3} ) =21[/tex]
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: [tex]y=-\frac{1}{2} (1.5)+\frac{7}{3}[/tex]
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))
