Question 53591
YOUR PROBLEM SAYS 50 NICKELS & DIMES. I BELIEVE YOU MEAN 150 NOT 50.
150=N+D & N=D+70 OR SUBSTITUTING (D+70) FOR N WE GET 150=(D+70)+D OR 
150=D+70+D OR 2D=150-70 OR 2D=80 OR D=80/2 OR D=40 THEN 150=N+40 OR N=150-40 OR N=110