A piece of ribbon is 16.32 m long. Mrs Li cuts off 40 cm of ribbon to make a bow. She then cuts the remaining ribbon into two pieces. One piece is 3 times as long as the other piece. Find the length of the longer piece of ribbon in metres.
Mrs Li cuts off 40 cm of ribbon, which is equal to 40/100 = <<40/100=0.4>>0.4 m.
So, the remaining length of the ribbon is 16.32 - 0.4 = <<16.32-0.4=15.92>>15.92 m.
Let's say the shorter piece of ribbon is x.
Then, the longer piece of ribbon is 3*x.
And we have the equation: x + 3*x = 15.92.
So, 4*x = 15.92.
Therefore, x = 15.92/4 = <<15.92/4=3.98>>3.98 m.
The longer piece of ribbon is 3*3.98 = <<3*3.98=11.94>>11.94 m long. Answer: \boxed{11.94}.