x = 3sqrt(x-4) looks like the equation of two separate functions, x and sqrt(x-4). You don't share the instructions (!), but I suspect that they ask you to find the x-value a which this equation is true.
One way of doing this (just an estimation) would be to graph y = x and also y = 3sqrt(x-4). Doing so will tell you quickly whether or not the graphs intersect. If they do intersect, you'll need to identify approx. the x-value at which this happens; that will be your "solution." If they don't intersect, no solution.
Please ask follow-up questions if these suggestions are not clear and sufficient.
Question #1: Do y = x and y = 3sqrt(x-4) ever intersect?
