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

7a + x = 4
x = 4 - 7a

then substitute the result (4 - 7a) into the second equation:

-2a - 5(4 - 7a) = -1
-2a + (-5 x 4) + (-5 x -7a) = -1
-2a - 20 + 35a = -1
-2a + 35a = -1 + 20
33a = 19
a = \( \frac{19}{33} \)
a = \(\frac{19}{33}\)

The circumference of a circle is the distance around its perimeter and equals π (approx. 3.14159) x diameter: c = π d. The area of a circle is π x (radius)² : a = π r².

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.

2a x 3b = (2 x 3) (a x b) = 6ab

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 - 4)(y - 1)
(y x y) + (y x -1) + (-4 x y) + (-4 x -1)
y² - y - 4y + 4
y² - 5y + 4

The area of a triangle is equal to ½ base x height:

a = ½bh
a = ½ x 2 x 4 = \( \frac{8}{2} \) = 4