Question 959277
The value of one loony is unknown.  Let L = fraction of dollar for 1 loony, which may be mixed or whole value.
Let x be how many loonies.

{{{system(L*x+0.25q+0.05n=18.3,q=x+3,n=2x)}}}
Three equations in four unknown variables, L, x, q, n.


{{{L*x+0.25(x+3)+0.05(2x)=18.3}}}


{{{L*x+0.25x+0.75+0.1x=18.3}}}


{{{L*x+0.35x+0.75=18.3}}}


{{{highlight_green(Lx+0.35x=17.55)}}}, not a linear equation.  Solutions must use x as a whole number.  L must be a positive real number RATIONAL



{{{(L+0.35)x=17.55}}}


{{{highlight_green(L+0.35=17.55/x)}}}, now this equation form allows picking any of several whole number values for x, and finding any fitting values for L.


{{{L=17.55/x-0.35}}}, and notice that there is a restriction here for x and for L, again, L must be positive.  Necessary, {{{0<x<=50}}}.