A circle has diameter of 22cm what is the radius

The radius is (half) the diameter.

Since you know the diameter = 22 cm,   of 22 = 11. So the radius = 11 cm

You could also use equations:      (d = diameter     r = radius)

d = 2r  --->           And plug in what you know

x = -3

y = -18

step-by-step explanation:

to solve by substitution, substitute one variable and solve for the other. then substitute again to find the remaining variable.

x-1/3(3x-9) = -3 since y=3x-9 substittute y.

x-1/3(3x-9)=-3

x + x +3 = -3

2x+3=-3

2x+3-3= -3-3

2x=-6

x=-3

substitute again into y=3x-9

y=3(-3)-9

y=-9-9

y=-18