The substitution method.
y = -4x + 15
-4x + 7y = 9

{y,x} = {3,3}

Step-by-step explanation:

1] y=-4x+15

[2] -4x+7y=9

Equations Simplified or Rearranged :

[1] y + 4x = 15

[2] 7y - 4x = 9

Graphic Representation of the Equations :

4x + y = 15 -4x + 7y = 9

Solve by Substitution :

// Solve equation [1] for the variable y

[1] y = -4x + 15

// Plug this in for variable y in equation [2]

[2] 7•(-4x+15) - 4x = 9

[2] - 32x = -96

// Solve equation [2] for the variable x

[2] 32x = 96

[2] x = 3

// By now we know this much :

y = -4x+15

x = 3

// Use the x value to solve for y

y = -4(3)+15 = 3

Solution :

{y,x} = {3,3}

see explanation

step-by-step explanation:

a

(6r + 7) + (13 + 7r) ( remove brackets and collect like terms )

= 6r + 7 + 13 + 7r

= 13r + 20

b

remove brackets and collect like terms

13 - r - 1 + r

= 12 - r

c

remove brackets and collect like terms

= - 8 - r + 2r - 4

= - 12 + r

d

remove brackets and collect like terms

= 7r - - - 6r

[-   - = - - = - ]

= r -