From (1) t = 10
So from (2) x + y = 10 ...(5)
Subtract (3) from (4) y2 - x2 = 28 or (y+x)(y-x) = 28 ...(6)
Use (5) in (6) to get y - x = 28/10 or y - x = 14/5 ...(7)
Add (5) and (7) to get 2y = 64/5 or y = 32/5
Subtract (7) from (5) to get 2x = 36/5 or x = 18/5
Can you take it from there?