Answer:
So, if we say Jiri's age is j (we can pick any letter), then Pamela's age is 2j, right?
j + 2j = 72
j is the same as 1j, but we wouldn't call you 1James, just James.
3j = 72
To isolate j, we do the opposite operation to both sides.
3j/3 = 72/3
j/j = 1, so that cancels out. 72/3 = 24.
j = 24
Jiri is 24 years old.