Why do this problem?
practises working systematically on addition and subtraction. This is a code, not algebra, and learners will need to try things out as well as working them out, so using trial and improvement will be essential.
Have you remembered that this is a code?
Have you thought of looking at the two number plates beginning with V?
Have you thought of writing out the alphabet and thinking of a way to turn the letters into numbers?
Can you think of a variation on the most obvious way of turning letters into numbers?
Learners who found this problem easy could try Ishango Bone
Suggest starting by writing out the numbers on the number-plates and adding up each one. Then write out the alphabet and think of a way of varying A = $1$, B = $2$ etc.