Question 501422
d = Dina's age
c = Cora's age
.
d+c = 30
so
d = 30-c
c = 30-d
.
Three years ago:
d-3 = Dina's age then
c-3 = Cora's age then
.
Cora was 3 times as old as Dina.
.
c-3 = 3*(d-3)
.
Substitute
.
(30-d) -3 = 3(d-3)
30 -d -3 = 3d -9
27 -d = 3d -9
36 = 4d
d = 9
.
c = 30-9
c = 21
.
Check your work?
3 years ago, was Cora 3 times Dina's age?
.
21-3 = 18
9-3 = 6
Yes.  3*6 = 18.
.
Answer:  Currently, Cora is 21 and Dina is 9.
.
Done.