What is the measurement of each of the interior angles of a regular quadrilateral? 90° 180° 60° 120°

  90°

Step-by-step explanation:

The regular quadrilateral is also known as a square. Its interior angles are right angles that measure 90°.

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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