Question 830139
<pre>
I assume you have something like this:

@--------------@--------------@--------------@--------------@--------------@
7              ?              ?              ?              ?             77

First find the distance from 7 to 77 by subtracting.

77-7 = 70

Divide that distance by 5 since there are 5 spaces, get 14.

Add 7+14, get 21.  Put 21 for the first question mark:

@--------------@--------------@--------------@--------------@--------------@
7             21              ?              ?              ?             77

Add 21+14, get 35.  Put 35 for the second question mark:

@--------------@--------------@--------------@--------------@--------------@
7             21             35              ?              ?             77

Add 35+14, get 49.  Put 49 for the third question mark:

@--------------@--------------@--------------@--------------@--------------@
7             21             35             49              ?             77

Add 49+14, get 63.  Put 63 for the fourth question mark:

@--------------@--------------@--------------@--------------@--------------@
7             21             49             49             63             77

Add 63+14, get 77.  You already have a 77 there, so you know it's correct.

Edwin</pre>