Assuming that the smallest measurable wavelength in an experiment is 0.730 fm (femtometers), what is the maximum mass of an object traveling at 927 m·s-1 for which the de Broglie wavelength is observable?

1 fm = 1.0 * 10-15 meters

so

0.610 fm x (1.0x10^-15 m / 1 fm)

= 6.1x10^-16 m

so the formula is

λ = h / mu

so,

as we know mass value so by putting

m = (6.626*10^-34) / (6.1*10^-16*199)

= (6.626*10^-34) / (1213.96 * 10^-16)

= 5.45 x 10^ - 21

hope thats an answer for you