Can u pls explain why A?
we know x is +ve and to keep things simple lets assume x=1
then to satisfy statement 1 the minimum value of z is > 5.5. If z= 5.5 then z-x = 4.5 and 10 -z is also equal to 4.5 which is incorrect
now avg of x and 10 in this case will be 5.5 and z>5.5.
lets consider another value for x i.e 9.8 [ keeping addition/division simple here :D]
then to satisfy stmnt 1, z will be greater than 9.90 as 10- z = 0.1 and z-x = 0.1 if z = 9.9.Avg of x and 10 will be 9.90 and z is greater than 9.90
hence statement 1 is sufficient. Hope this helps.