Answer:
20 cm
Explanation:
triangle
30/3=10=a
rectangle
30-20=10/2=5=b
square
4 times 5=20
25
3a=30... equation 1
2a+2b=30... equation2
equation 2 => a+b=15 ... equation 3
equation 1 => a = 10 ... equation 4
equation 4 & equation 3 => b = 5
5^2 = 25
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