J - Jan's age
T - Tritt's age
(1) J + 3 = 2T
(2) J + T = 30 |subtract T from both sides
(2) J = 30 - T
subtitute (2) to (1)
30 - T + 3 = 2T
33 - T = 2T |add T to both sides
3T = 33 |divide both sides by 3
T = 11
subtitute the value of T to (2)
J = 30 - 11
J = 19
Answer: Jan is 19 and Tritt is 11.