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

6b + x = 4
x = 4 - 6b

then substitute the result (4 - 6b) into the second equation:

8b - 7(4 - 6b) = 9
8b + (-7 x 4) + (-7 x -6b) = 9
8b - 28 + 42b = 9
8b + 42b = 9 + 28
50b = 37
b = \( \frac{37}{50} \)
b = \(\frac{37}{50}\)

To multiply binomials, use the FOIL method. FOIL stands for First, Outside, Inside, Last and refers to the position of each term in the parentheses:

(y + 1)(y + 2)
(y x y) + (y x 2) + (1 x y) + (1 x 2)
y² + 2y + y + 2
y² + 3y + 2

When solving an equation with two variables, replace the variables with the values given and then solve the now variable-free equation. (Remember order of operations, PEMDAS, Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.)

The formula for circumference is circle diameter x π:

c = πd
c = 14π

The Pythagorean theorem defines the relationship between the side lengths of a right triangle. The length of the hypotenuse squared (c²) is equal to the sum of the two perpendicular sides squared (a² + b²): c² = a² + b² or, solved for c, \(c = \sqrt{a + b}\)