Question 78788
Let M = Mary's present age.
Let B = One twin's present age.
Let W = Other twin's present age.
From the problem description, you can write:
M = B+3 and
(M+1)+(B+1)+(W+1) = 102  Why +1?  Because next year they will all be 1 year older than they are now.  Now substitute for the M = B+3, and since B=M (Twins would be the same age), you can rewrite the equation:
(B+3)+1 + B+1 + B+1 = 102 Simplify and solve for B
3B + 6 = 102 Subtract 6 from both sides.
3B = 96 Divide both sides by 3.
B = 32
The solution is:
Mary's age is 32+3 = 35 years.
One twin is 32 years.
The other twin is 32 years.

Check:
(M+1)+(B+1)+(W+1) = (35+1)+(32+1)(32+1) = 36+33+33 = 102 The sum of their ages next year.