First of all, we have to assume that this question is talking about this year -- in other words it is this year that they have been married 31 years.
If that is that case, they you just have to subtract 31 from this year. 2010-31 = 1979. So they were married in 1979. However, if their anniversary has not come yet this year then they were married in 1978 and when their anniversary gets here, they will have been married for 32 years.
You figure out their daughter's birth year the same way. 2010 - 19 = 1991.