D. 35 is the answer. Since we know that 14=2k based on the knowledge given in the first part of the equation, we can solve for K. We learn that K=7. Then, we can substitute K into the second equation: y=(7)(5) which is 35.
2n+14=14+2n so this one as an infinite number of solutions. The second one 1-x=-x-6 so you add x on both sides which results in it having no solutions.