Question 51154
say the input is "x"(cuz input is variable)
so we will build up the equation

so the out put is 5 more than 2times the input,
therefore 2 times input, means 2x and 5 more, means 5 should be added with the 2 times input
 therfore we get the equation   2x+5 = output.

Cheers we hav come up with the equation. So substitude this equation in the question.  
              2x+5= output
therefore     2x+5=17
                2x= 17-5
                 x= 12/2
                  = 6