Ineed to know how to write and solve the equation

Barney & noblet customers can choose to purchase a membership for $25 per year members receive 10% off all store purchases 1. how much would a member pay per year if he bought $50 worth of items each year? 2. write a slope-intercept equation that expresses how much a member pays per year using x to represent his purchases per year 3. how much would a member have to spend per year to pay off his membership fee?

Hey free points ! people i have a few math questions on my profile consider looking at them i have to get done in 30 mins!

What is the value for this expression? 2e-5