To determine you repeatedly replace the larger of the two numbers by the remainder of the larger divided by the smaller .. until the lager is a multiple of the smaller. In your case I get

The last equality sign holds, because 4005 is a multiple of 1335.

Just remember that2) find the Lowest Common Multiple of 54735 and 238965

3) find the solution to the linear congruence 54735a + 238965b = 16020

and finally explain why there are an infinite number of solution to this linear congruence and find one more solution?