Is the following relation a function? {0.3,0.6), (0.4,0.8), (0.3,0.7), (0.5,0.5)}

Keep in mind the definition of a function. For 2 points, (x,y) and (x,z) it is a function only if y = z. 
Because you have the points {0.3,0.6} and {0.3,0.7}, for it to be a function, 0.6 would have to equal 0.7. Since this is clearly false, it is not a function. 

If cheese is $4.40 per kilogram, you should pay .88