Question 757168
P = patty's age now  T = terry's age now

Patty is 3 times as old as terry.  3T = P
In 10 years the sum of their ages will be 36. (T+10) + (P+10) = 36

Now substituting/replacing the P in the second equation with 3T from the first equation we get
(T+10) + (3T+10) = 36

Now we combine like terms and then solve for T

(T+3T) + (10+10) = 36
4T + 20 = 36  
4T = 16
T = 4
P = 3T = 3(4) = 12