This is a question about comparison The length ratio of the three sides of a triangle is 3:4:5. The shortest side is 3 cm. What is the longest side of the triangle?

This is a question about comparison The length ratio of the three sides of a triangle is 3:4:5. The shortest side is 3 cm. What is the longest side of the triangle?

3+4+5=12
3 △ 3 / 12 × 5 / 12 = 5 (CM)

A math problem of grade five in primary school, it's urgent!
For a kiwi fruit, it costs 2.9 yuan per box, 41 yuan per box for the whole box, and 15 pieces per box. How much is the average price per box for the whole box? Which method is cheaper, the whole box or the single box?
Two questions, must have the detailed computation process, otherwise I cannot understand
Good reward

29 / 10 yuan for a single box, 41 / 15 yuan for a whole box, 87 / 30 yuan and 82 / 30 yuan after sharing
A: the whole box is cheap

Some mathematical formulas of geometric area (to be explained)
I want some formulas of mathematical geometric area. The more complete the formula, the better

Square s = side length & sup2; rectangle s = length × width triangle s = bottom edge × height on the bottom edge △ 2; parallelogram s = bottom edge × height trapezoid on the bottom edge s = (upper bottom + lower bottom) × height △ 2; circle s = circumference × radius & sup2; ellipse s = circumference × length of long half axis × length of short half axis, sector s = angle of the sector △ 2