Question

Evaluate the expression when y= 7 and x = 9.
x + 4y

Answer 1

[1] 9x - 4y = 7

[2] x - 4y = -17

[2] x = 4y - 17

// Plug this in for variable x in equation [1]

[1] 9•(4y-17) - 4y = 7

[1] 32y = 160

// Solve equation [1] for the variable y

[1] 32y = 160

[1] y = 5

// By now we know this much :

x = 4y-17

y = 5

// Use the y value to solve for x

x = 4(5)-17 = 3

Explanation:

Answer 2

9+4(7)

Explanation:

Start by replaceing y with 7

Do the same with x