The area of a rectangle is equal to its length x width:

a = l x w
a = a x b
a = 3 x 7
a = 21

A circle is a figure in which each point around its perimeter is an equal distance from the center. The radius of a circle is the distance between the center and any point along its perimeter. A chord is a line segment that connects any two points along its perimeter. The diameter of a circle is the length of a chord that passes through the center of the circle and equals twice the circle's radius (2r).

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 5 x 8) + (2 x 8 x 8) + (2 x 5 x 8)
sa = (80) + (128) + (80)
sa = 288

You need to find the value of b so solve the first equation in terms of y:

9b + y = 3
y = 3 - 9b

then substitute the result (3 - 9b) into the second equation:

7b - 7(3 - 9b) = 1
7b + (-7 x 3) + (-7 x -9b) = 1
7b - 21 + 63b = 1
7b + 63b = 1 + 21
70b = 22
b = \( \frac{22}{70} \)
b = \(\frac{11}{35}\)

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

7a - 6a = 1a