Question 847433
Let 

A = Ana's age
L = Lisa's age



"Ana's age is 4 more than Lisa's age"


turns into


Ana's age = (Lisa's Age) + 4


Now replace those phrases with what they defined by (see above) to get


A = L + 4


-------------------------------------------------------


So lisa is L years old and ana is L+4 years old.


Add the two ages


(Ana's age) + (Lisa's age)


(L+4) + (L)


L + 4 + L


(L + L) + 4


<font size = 5 color="red">2L + 4</font>


is the sum of their two ages