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.

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 coordinate grid is composed of a horizontal x-axis and a vertical y-axis. The center of the grid, where the x-axis and y-axis meet, is called the origin.

The perimeter of a triangle is the sum of the lengths of its sides:

p = x + y + z
p = 15cm + 5cm + 15cm = 35cm

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

5b + z = 2
z = 2 - 5b

then substitute the result (2 - 5b) into the second equation:

-b + 1(2 - 5b) = -8
-b + (1 x 2) + (1 x -5b) = -8
-b + 2 - 5b = -8
-b - 5b = -8 - 2
-6b = -10
b = \( \frac{-10}{-6} \)
b = 1\(\frac{2}{3}\)