$717=K+99 \quad K=$

Step 1 ：Translate the equation $717=K+99$ into English: 717 equals K plus 99.

Step 2 ：Subtract 99 from both sides of the equation to isolate K: $717 - 99 = K$

Step 3 ：Calculate the value of K: $K = 618$

Step 4 ：Final Answer: \(\boxed{618}\)