In order to find the values of x and y, consider that the triangles are similar. Then, the proportion between similar sides of the triangles are equal.
In triangles ABC and DEF you have:
EF/BC = ED/BA
by replacing the values of such sides you obtain:
x/28 = 7/14 multiply by 28 both sides
x = (7/14)(28)
x = 14
Hence, the value of x is x = 14
Next, for the same triangles use the following proportion:
AC/DF = BC/EF
by replacing the values of such sides you obtain:
y/10 = 28/14 multiply by 10 both sides
y = (28/14)(10)
y = 20
Hence, the value of y is y = 20