Answer: 
Step-by-step explanation:
Given
The top left and right corners measures
and the bottom right corner measures
.
Suppose the missing corner measures 
So, the sum of the four angles of parallelogram is 

Therefore, the missing angle is
.
88.3 is what % of 21
21 × a percent = 88.3
Divide 21 on either sides to find the percentage.

=

% = 4.204
88.3 is 4.205% of 21
I would try but it wont let me.
Assignment: 
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Answer: 
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Explanation: 
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[ Step One ] Follow PEMDAS Order Of Operations; Calculate Within Parenthesis
Note: 

[ Step Two ] Rewrite Equation

[ Step Three ] Calculate Within Parenthesis

[ Step Four ] Rewrite Equation

[ Step Five ] Calculate Exponents

[ Step Six ] Rewrite Equation

[ Step Seven ] Multiply

[ Step Eight ] Rewrite Equation

[ Step Nine ] Subtract

[ Step Ten ] Rewrite Equation

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Answer:
30 or younger
Step-by-step explanation: