Why total revenue curve is upward slopping straight line and a marginal revenue curve is also price line?

The total revenue curve is an upward-sloping straight line because total revenue (TR) is calculated as price (P) multiplied by quantity sold (Q), or TR = P × Q. In a perfectly competitive market, since the price remains constant as additional units are sold, the total revenue increases linearly with each additional unit sold. The marginal revenue (MR) curve is also a price line in this context because, under perfect competition, the revenue gained from selling one more unit (marginal revenue) is equal to the market price, remaining constant regardless of the quantity sold.