(a) the fact there a set of input values is mapped to a set of output values without assigning multiple output values to one input makes this table (and a set of data) a function
(b) a case of two assignments of same input value to two different output values could cause this table to not be a valid function. Example: add a row in the table as follows:
Input: 3 Output: 11
which means a 3 would be mapped to both 5 and 11
(c) the function could be like this:
f(k) = 2k - 1
Test that it works for the values in the table:
f(3) = 2*3-1 = 5
f(4) = 2*4-1 = 7
f(6) = 2*6 -1 = 11
I let you do the last one!
