let
x------> amount of money Theo has
y------> amount of money Denise has
z------> amount of money Rudy has
we know that
x+y+z=$45-----> equation 1
x=5+y-----> equation 2
y=11+z----> equation 3
substitute equation 2 in equation 1
[5+y]+y+z=45-------> 2y+z=40-----> equation 4
y=11+z----> equation 3
2y+z=40-----> equation 4
resolves the equations system
using a graph tool
see the attached figure
the solution is
y=17
z=6
x=5+y----> x=5+17----> x=22
the answer is
Denise has $17
