A triangle is a three-sided polygon. It has three interior angles that add up to 180° (a + b + c = 180°). An exterior angle of a triangle is equal to the sum of the two interior angles that are opposite (d = b + c). The perimeter of a triangle is equal to the sum of the lengths of its three sides, the height of a triangle is equal to the length from the base to the opposite vertex (angle) and the area equals one-half triangle base x height: a = ½ base x height.

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

-9b + y = 6
y = 6 + 9b

then substitute the result (6 - -9b) into the second equation:

9b - 9(6 + 9b) = -7
9b + (-9 x 6) + (-9 x 9b) = -7
9b - 54 - 81b = -7
9b - 81b = -7 + 54
-72b = 47
b = \( \frac{47}{-72} \)
b = -\(\frac{47}{72}\)

A parallelogram is a quadrilateral with two sets of parallel sides. Opposite sides (a = c, b = d) and angles (red = red, blue = blue) are equal. The area of a parallelogram is base x height and the perimeter is the sum of the lengths of all sides (a + b + c + d).

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.

2a + 2a = 4a

The surface area of a cylinder is 2πr² + 2πrh:

sa = 2πr² + 2πrh
sa = 2π(2²) + 2π(2 x 2)
sa = 2π(4) + 2π(4)
sa = (2 x 4)π + (2 x 4)π
sa = 8π + 8π
sa = 16π