The perimeter of the rectangle (according to the image) is the base × 2 added to the height × 2. 6 × 2 = 12, and 4 × 2 = 8, giving you 20cm. We have to subtract 6cm because that side is connected to the semicircle, so you get 14cm. The perimeter of the curved part of the circle is also known as the circumference, and the formula for that is π × diameter, which in this case is 6. We need to use 3.14 as pi, so 3.14 × 6 = 18.84. Because it's a semicircle, we need to divide by 2 to get 9.42cm. Now we just add them all up (9.42 + 14) to get your final answer as 23.42cm. I hope this helps! Sorry it was so long :)
For anything to do with force you have to assume an even amount of force is spread out evenly. But for things like growing rate you have all those variables so you can't assume a constant growing rate like acceleration.
