Answer:
• for x = 2a√t, make t the subject:
[tex]{ \tt{x = 2a \sqrt{t} }} \\ \\ { \tt{ \sqrt{t} = \frac{x}{2a} }} \\ \\ { \boxed{ \tt{t = \frac{ {x}^{2} }{4 {a}^{2} } }}}[/tex]
• then find y:
[tex]{ \tt{y = {ar}^{2} - 2at}} \\ \\ { \tt{y = {ar}^{2} - 2a( \frac{ {x}^{2} }{4 {a}^{2} } ) }} \\ \\ { \boxed{ \tt{y = {ar}^{2} - \frac{ {x}^{2} }{2a} }}}[/tex]