A rectangle is a parallelogram containing four right angles. Opposite sides (a = c, b = d) are equal and the perimeter is the sum of the lengths of all sides (a + b + c + d) or, comonly, 2 x length x width. The area of a rectangle is length x width. A square is a rectangle with four equal length sides. The perimeter of a square is 4 x length of one side (4s) and the area is the length of one side squared (s²).

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

3a + y = -6
y = -6 - 3a

then substitute the result (-6 - 3a) into the second equation:

-9a + 7(-6 - 3a) = -1
-9a + (7 x -6) + (7 x -3a) = -1
-9a - 42 - 21a = -1
-9a - 21a = -1 + 42
-30a = 41
a = \( \frac{41}{-30} \)
a = -1\(\frac{11}{30}\)

A trapezoid is a quadrilateral with one set of parallel sides.

An acute angle measures less than 90°, a right angle measures 90°, and an obtuse angle measures more than 90°.

An exterior angle of a triangle is equal to the sum of the two interior angles that are opposite:

d° = b° + c°

To find angle c, remember that the sum of the interior angles of a triangle is 180°:

180° = a° + b° + c°
c° = 180° - a° - b°
c° = 180° - 42° - 48° = 90°

So, d° = 48° + 90° = 138°

A shortcut to get this answer is to remember that angles around a line add up to 180°:

a° + d° = 180°
d° = 180° - a°
d° = 180° - 42° = 138°