Final answer:
To print the desired sequence of numbers, the increment value for the variable 'x' in the loop should be 5.
Step-by-step explanation:
To make the loop print the numbers 55, 60, and 65 in succession, you need to increment the variable x by 5 in each iteration of the loop. Therefore, the value that should replace the blank (____) in the code snippet is 5. This can be confirmed by considering the starting value of x, which is 50, and noting that adding 5 to 50 gives 55, then 60, and finally 65 in the subsequent iterations.