Jiri's age is 20
Let Pamela's ae be P and Jiri's age be J
From the equation;
P = J + 5 ...............(i)
This is as Pamela is 5 years older
Adding their ages, we have 45
P + J = 45 ........................(ii)
Substitute i into ii
J + 5 + J = 45
2J + 5 = 45
2J = 45-5
2J = 40
J = 40/2
J = 20