3. If you add -10 to 4 times the mystery number you get 0. What is the Mystery Number? 4. The Links phone company charges has a free smartphone (y-intercept : O) but $60 per month (rate of change). The Connections phone company charges S300 for the smartphone (y-intercept) and s40 per month (rate of change). a. Write an equation in slope intercept form for each company. (y : mx + b) b. Write an equation to find out how many months each company will take to get to a cost of S900 total. (re-write each equation, but replace the y with 900) c. SOLVE each equation. SHOW each step.