Solving for a variable means to rewrite the equation so that the desired variable is alone on one side. So, we have to "move" all the other variables/constants in order to make this happen. We are allowed to add/subtract the same quantity from both sides, or to multiply/divide both sides by any non-zero number.
Let's start with the first example: we are given
11. 
the variable
is not alone on the right hand side because it is multiplied by
. We can reverse this by dividing both sides by
: the equation becomes

So, we have written the equation as
, which means that
now sits alone on one side of the equation, and thus we have solved the equation for
!
Similarly, we do all the others:
12. 
Subtract
from both sides to get

13. 
Subtract
from both sides to get

Now divide both sides by
to get

14. 
Multiply both sides by 2:

Divide both sides by
:

Answer:
y=-1x-6
Step-by-step explanation:
F(x)=125-(125*0.2x)
to find the value of the phone after 3 years, you put x=3.
f(3)=125-(125*0.2(3))
f(3)=50
Step-by-step explanation:
3(x - 4y) - 2(y + 7x)
= 3x - 12y - 2y - 14x
= 3x -14x -12y -2y
= -11x -14y