If a skydiver falls 144 feet in 3 seconds in you need to find the time per second that they’re falling, you would simply have to get the time per one second. You have to get the 3 to one, so you would divide by 3 on both sides, getting 48 feet per second. (assuming they fell at the same rate all 3 seconds)
Multiples of 15 are: 15,30,45,60,75,90,105,120,135,150,165,180,195,210,225,240,255,270,285,300,315,330,345,360,375,390,405,420,435,450,465,480,495,510,525,540,555,570,585,600,615,630,645,660,675,690,705,720,735,