Theresa is 14 years younger than her brother. Together, their total age in years is 35.

Let:

T = Theresa age

H = her brother

We know:

T = H - 14

T + H = 35

Substitute T

H - 14 + H = 35

2H - 14 = 35

2H = 49

H = 49/2 = 24.5

Since we know H = 24.5 we then can substitute it to either equation.

T = H - 14

T = 24.5 - 14

T = 10.5

Theresa is 10.5 years old

Her brother is 24.5 years old