comprehension in collile

see shankara!!!!!!!!!!with or without da wall da max. height will be da same!!!!!!!!!!!
u^2sin2α/g = 5d,,,,,,,,,,(1)
u^2sin^α/2g=h ........(2)...............
(1)/(2)...............4cosα/sinα=5d/h.....
h=5dtanα/4.................................

q17........horizontal distance travelled will be da same.............

5d = n*d/2.......
n = 10 but da last collision it comez bak to da ground so nt counted so 10-1=9.........

q18 is evidently zero!!!!!!!!!!!!!!!!!!!!!!!!!!!
correct me if im rong!!!!!!!!!!!!!!!!!!!!