31.5cm Multiply 20 times 5 then add 1.5 cm because there are 20 days and the plan is to get to 5cm high. The plan only grows 1.5cm per day so 31.5cm would be ur answer
therefore angle Y will be equal to angle X by vertically opposite angle as by taking all the angles inside the traingle will be equal to Y so Y = X = 60°