Ten times the square root of a nonzero number is equal to forty times the number

Hello : 
let : x this number 
 10√x = 40 x x > 0
√x = 4 x  and : x > 0
(√x )²= (4 x)²  and : x > 0
x = 16 x²   x > 0 : i'can simplifiy by : x 
1 =16x
x = 1/16

No solution : there is no number of boxes that she bought