Specifying "step 3 to step 4" depends on what level of detail is being shown.  I like to start a solution with 'a few steps' and only increase the number of solution steps when the additional steps are helpful. 

The inquiry probably involves simplification [or creation] of a complex fraction.  The denominator is a simple expression "6t^3" while the numerator is the fraction "3/t^2" since t^(-2) is "1/t^2" as a positive exponent and becomes the denominator of the upper portion of the complex fraction.