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.

4a + 5a = 9a

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

9c + y = 6
y = 6 - 9c

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

8c - 1(6 - 9c) = -8
8c + (-1 x 6) + (-1 x -9c) = -8
8c - 6 + 9c = -8
8c + 9c = -8 + 6
17c = -2
c = \( \frac{-2}{17} \)
c = -\(\frac{2}{17}\)

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).

Angles around a line add up to 180°. Angles around a point add up to 360°. When two lines intersect, adjacent angles are supplementary (they add up to 180°) and angles across from either other are vertical (they're equal).

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

a = ½bh
a = ½ x 4 x 1 = \( \frac{4}{2} \) = 2