Part (A)
We have two congruent right triangles with base and height of 5 and 3
Let's find the area of one triangle.
area = 0.5*base*height = 0.5*5*3 = 7.5
That's the area of one triangle.
Double it to get the total area of 2*7.5 = 15.
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Or another method is to use the area of a parallelogram formula
area = base*height
area = 3*5
area = 15
Answer: 15 square cm
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Part (B)
Focus on one of the four congruent right triangles.
Use the pythagorean theorem with a = 2 and b = 4 to find the hypotenuse c.

The unshaded inner square has side lengths of
centimeters.
The area of the unshaded inner region is
square cm.
The entire square is 6 cm by 6 cm (since 2+4 = 6). This larger square has area 6^2 = 36
The shaded area is the difference of these two regions
36 - 20 = 16
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Another approach
area of triangle = 0.5*base*height
area = 0.5*2*4
area = 4
One shaded triangle has area 4 square cm. Quadruple this because we have 4 congruent right triangles with the same area as each other.
4*4 = 16 is the total shaded area
Answer: 16 square cm
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Part (C)
m = area of larger square
m = 5*5
m = 25 square cm
n = area of unshaded smaller square
n = 2*2
n = 4 square cm
p = shaded area
p = difference of m and n
p = m - n
p = 25 - 4
p = 21
Answer: 21 square cm