SOLVE for Function Vectors

[NomadVehr]

I made a program that returns VECTOR(x) expressed as [a(x),b(x),c(x)]
given that b(x) is a known value, what would be the sintaxis for solving VECTOR(x) for x with a(x), b(x) or c(x) known?

On the specifics side this is the curve for a pump, where a(x) is the head, b(x) the efficiency and c(x) the shaft power.

At any given time and generally the easiest to know would be the head. So based on the head only known I would like to know how to use the solve function in the case of a vector.

I currently have the functions as separate, but I would like to see if I can simplify this.

Thanks in advance.