Find the equation of the line tangent to graph f

I need to find an equation of the line that is tangent to the graph of f and parallel to the given line.

Function:

f(x)=(x^3)+2

Line:

3x-y-4=0

So far I rearranged the equation of the line to get... y=3x-4

So I plugged lines with the slope of 3 into my calculator. The graph y=3x seemed to look tangent to f(x) and parallel to the line. However, I need to solve this problem without a calculator, and without guessing by the looks of a graph.

Thanks to anyone who tries to help me.

--Cori