Final answer:
Without a clear diagram or additional context, we cannot definitively solve for the value of 12 in terms of A. We need more information on how /1, 13, and 12 are related to each other.
Step-by-step explanation:
The student's question, which asks about locating a number in a shaded part of a diagram, appears incomplete as the diagram is not provided. However, interpreting the question with available information, if /1 = 5 A and 13 = -2 A, then we can find the value of 12. We have two equations with presumably a relationship between the indexes (like /1, 13, and 12 referring to some sequence or parameters being referred to as A). Without further context, we cannot find a definitive value for 12, but we can deduce that it's another expression in terms of A. In order to solve this problem, more information is required, specifically the relationship between these terms. Otherwise, we can only hypothesize that 12 will be some multiple of variable A, which could be represented as 12 = k A, where k is some constant.