In a walk for charity you walk at a rate of 100 meters how long does it take you to walk 2

Adepartment store purchases screen-printed t-shirts at a cost of $5 per shirt. they mark up the price 150% (making the selling price 250% of the store's purchase price) and put them on the sales floor. every month that a t-shirt doesn't sell, the store reduces the selling price by 25%.

Determine the solution for mc001-1.jpeg

Math i have no idea how to do a and b