At a back to school sale chris bought 3 pencils and 7 pens for $3.55. at the same sale his brother james bought 7 pencils and 3 pens for $2.95. how much would it cost to purchase 1 pencil and 1 pen?

Let a represent pencils and b represent pens. Then we can create the equations: 3a + 7b = 3,55 and 7a + 3b = 2,95. Isolate the a in the first equation: a = (3,55-7b)/3 and put the isolated a into the second equation: 7(3,55-7b)/3 + 3b = 2,95 => 7*3,55/3 - 7*7b/3 + 3b = 2,95 => 7*3,55/3 - 2,95 = 49b/3 => b = 5,333/16,333. To find a put the value of b into the first equation: 3a + 7*5,333/16,333 = 3,55 => a = 0,42146 and b=5,333/16,333= 0,32652

In all honesty, there really is no “work” per say to show. mainly it’s just using the process of elimination. the question is asking which domain(s) would be the most appropriate for the function c(n). n is the number of observed vehicles so right away, 1, 2, and 3 can be eliminated.why? 1, 2 start in the negatives and therefore it is impossible to observe negative cars. so, #4 would be the best answer to the given problem.