Suppose you have a quad$-$core computer that can execute four processes simultaneously $($one process on each core$).$ Suppose there is a program in which $40\%$ of the total execution time must be executed sequentially but the remainder can be divided into $6$ equal parts that can be executed concurrently.

What is the maximum speedup you can get using all four cores over using one core. Clearly explain your answer. No points for simply putting down a numerical answer without an explanation, even if correct.