Open a table with x_1, enter the data, then type the model with subscripted parameters — y_1 sim m x_1 + b for a line, y_1 sim a b^x_1 for an exponential — and Desmos returns the best-fit parameters and R^2. Whenever an item gives a table and asks for a line of best fit, a slope, or a predicted value, use regression; never compute it by hand.