Can someone me with this and explain how to solve it essentially?

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Well for the first equation you plug in the numbers for the variable of pi and r. Since the value of pi is 3.142 and the value of r is 5. You plug it in to the equation like this, C=2(3.142)(5). Then whatever you get then is your answer for the first part. 

For the second equation you basically do the what you did in the first equation. You plug in the values for the variables of pi and r. Which are also 3.142 and 5. Therefore the equation would look like this, A=(3.142)(5)^2. And then when you multiply it whatever you get is your answer.

the law of definite proportions states samples of a compound will always contain the same proportion of elements by mass. in other words, a given compound will always contain the same elements in the same proportions by mass.the law of multiple proportions states when two elements combine with each other to form more than one compound, then the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.