Create a Turing Machine in JFLAP (over the alphabet {a,b,#}) that takes a string with one # in it and swaps the strings on either side of the #. If the string is a legal start string then the machine halts pointing at the # when it's done. If it's not a legal start string then the machine should not accept the string (i.e. don't go to the halt state) but otherwise it can do whatever you like...

4 GHz

Explanation:

Time taken for computer A to execute the program is = 10 secs

Given frequency of the clock for computer A is = 2 GHz

We know Clock period = 1 / frequency = 1 / 2 * 109 = 0.5 ns

Number of clocks requried to execute the program in computer A is

= Total Execution time / clock period = 10 / 0.5 * 10-9 = 20 * 109 clocks

Given Time taken for computer B to execute the program is = 6 secs

Given computer B requries 1.2 times as many clocks as computer A

implies number of clocks to execute program in computer B = 1.2 * 20 * 109 = 24 * 109

Here clock period of computer B = Total execution time / number of clocks

                               = 6 secs / 24 * 109

                               = 0.25 ns

Hence clock rate = frequency is = 1 / clock period = 1 / 0.25 ns = 4 GHz.