Inradius of a triangle from its sides: r = area / semi-perimeter

This type of question, asked 2 times: CDS 1 2022, CDS 1 2023. All 2 questions below, oldest first.

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Question 1
CDS 1 2022
88 $What is the radius of the circle inscribed in a triangle whose sides are 4 cm, 7.5 cm and 8.5 cm?$
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Question 2
CDS 1 2023
61 $What is the area of the circle (approximately) inscribed in a triangle with side lengths 12 cm, 16 cm and 20 cm ?$
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