you can turn 3.6 into a fraction, and then switch the numerator and denominator: 3.6 = 3.6/1 = 36/10
the reciprocal is
10/36 = 5/18
reduced the fraction by dividing the top and bottom by 2
you could ALSO say the reciprocal of:
3.6/1 is 1/3.6,
but i assume you're supposed to come up with a nice fraction...