Extracting an unknown variable from a formula

Hello,

I really don't know how to name this, but here is what I'm trying to do:

Let's say cos(2*mt+phi)= -sin(b)/sin(phi);

Is there a function in Mathcad Prime 3 that can extract "mt" from the equation and deliver it like : mt = 2 arccos (2*phi)/-sin(b)*sin(phi)? (this is just an example)