hi can help explain iii , why can’t equate to positive 7 ? why can’t equate to 15 ? why can’t equate to 8 ? then minus to get the gap ? pls help answer all qns if possible ...

thanks WAi Mun . upon reading ur ans again , i can understand . first is , when time is 0 , x will be 0. Then when x is 0 , y will be 0. hence , left of ramp point is (0,0). hence , rightmost of ramp encounters height drop of 7cm . means new height = 0-7 = -7. then we find x value when y=-7