Perimeter is equal to the sum of the four sides:

p = a + b + c + d
p = 9 + 2 + 8 + 4
p = 23

A rectangle is a parallelogram containing four right angles. Opposite sides (a = c, b = d) are equal and the perimeter is the sum of the lengths of all sides (a + b + c + d) or, comonly, 2 x length x width. The area of a rectangle is length x width. A square is a rectangle with four equal length sides. The perimeter of a square is 4 x length of one side (4s) and the area is the length of one side squared (s²).

You need to find the value of c so solve the first equation in terms of z:

4c + z = 2
z = 2 - 4c

then substitute the result (2 - 4c) into the second equation:

-7c - 5(2 - 4c) = 3
-7c + (-5 x 2) + (-5 x -4c) = 3
-7c - 10 + 20c = 3
-7c + 20c = 3 + 10
13c = 13
c = \( \frac{13}{13} \)
c = 1

The surface area of a cube is (2 x length x width) + (2 x width x height) + (2 x length x height):

sa = 2lw + 2wh + 2lh
sa = (2 x 1 x 6) + (2 x 6 x 4) + (2 x 1 x 4)
sa = (12) + (48) + (8)
sa = 68

To multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

(4a)(9ab) - (9a²)(4b)
(4 x 9)(a x a x b) - (9 x 4)(a² x b)
(36)(a¹⁺¹ x b) - (36)(a²b)
36a²b - 36a²b
0a²b