Explanation:
Your question isn't clear. But if you are trying to find the value of 3P, with P correlating with any of Z, G, K, or B, then you have to first obtain what these values are.
5Z = 13
=> Z = 13/5
4G = 11
=> G = 11/4
8K = 91
=> K = 91/8
9B = 11
=> B = 11/9
But we don't know what 3P is related to, it would've been easy to make substitutions and obtain the required solution.