If we are to express the linear equation in slope-intercept form wherein the slope is the cost per download and y is the total cost. The answer should be,
Website 1: slope = 1.5 and y-intercept = 30
The equation that would represent the given is,
y = 1.5x + 30
Website 2: If we consider that there is no additional cost for this except for the cost per downloaded music then, the equation would be,
15% of 45 is 0.15 x 45 or 6.75 feet. That's how far the submarine descended in 1 minute. So, in 4 minutes the submarine would be 4 x 6.75 feet down which is 27 feet.