1) sqrt(0.25) = 0.5 y=0.5m
2) sqrt(1) = 1; y=1m
3) sqrt(2.25) = 1.5; y=1.5m
4) sqrt(4) = 2; y=2m
For the graph part you need to plot these points:
(0.25,0.5)
(1,1)
(2.25,1.5)
(4,2)
and then if we take a look at the line made, we can see that it is curved which means the function is not linear