Let

x = Nadia's age now, x>0

y = William's age now, y>0

Nadia is 36 years younger than William:

x = y - 36

Fourteen years ago, William was 5 times as old as Nadia:

y - 14 = 5(x - 14)

We have the following system of equations:

x = y - 36

y - 14 = 5(x - 14)

........

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x = 23 years

y = 59 years

Nadia is 23 years old now.

William is 59 years old now.