Y= 2x - 3 y = 4x + 1 2x - 3 = 4x + 1 what do i do next to get -2x = 4?

Y = 2x - 3 (1)
y = 4x + 1 (2)


Equation (2) - (1) :

(y - y) = (4x + 1) - (2x - 3)
0   = 4x + 1 - 2x + 3             // remove brackets
0 = 2x + 4                            // combine like terms
2x + 4 = 0                            // switch sides
2x = -4                                 // take away 4 from both sides
x = -2 sub into (1)        // Divide by 2 on both sides

y = 2(-2) - 3                          // Sub x = -2 into equation (1)
y = -4 - 3                               // Remove bracket
y = -7                                     // Combine like terms


x = -2,  y = -7

100 square tiles cause its perimeter of a rectangle.
Note: I am assuming a square tile is equal to a foot, and it probably is based on how the question is worded.