If you multiply 48cm times 15cm,you get 720cm.Which would leave you with 60 left because 780 minus 720 equals 60.The height of the other base is 60cm.
X = 2y
2x + 2y = 24
So if x = 2y that means 2x = 4y. Which means that 2x + 2y = 24 can be written as 4y + 2y = 24. Simplified to 6y = 24. Now we need to get 1y so we divide both sides by 6, 6y/6 = y and 24/6 = 4. so y = 4. so x= 2y can be written as x = 8.