Question

pls it is very urgent pls give me the answer

Answer 1

Given ratio = 13 : 3 : 12.

           Total = 13 + 3 + 12

                    = 28.

The percentage of carbon = 3/28 * 100

                                             = 10.7.

Answer 2

this type of problems is known as convert each term of ratio to percentage

first you have to add all the number they are 13+3+12
the answer is 28
now you have to find the percentage of the part of carbon out of 28

so write it in this way:
2 upon 28*100
=7.14%