A 3:45 marathon is 8:35 per mile, or 5:20 per kilometer, for 26.2 miles: 10K in 53:19, halfway in 1:52:30 and 20 miles in 2:51:38. It sits halfway between a 3:30 marathon and a 4 hour marathon in pace as well as time, about 34 seconds per mile from each.
The exact pace is 8:34.9 per mile, so the rounded 8:35 misses: held all the way, it finishes in 3:45:03. 8:34 per mile finishes in 3:44:36, and 8:30 per mile in 3:42:52. Per kilometer, 5:20 finishes in 3:45:02 and 5:19 per km breaks it in 3:44:20.
On a treadmill the goal lines up with a round setting. 7.0 mph is 8:34 per mile, just inside the pace that breaks 3:45; held for 26.2 miles it would finish in 3:44:44. 6.9 mph is 8:42 per mile, too slow. The treadmill pace chart has every other speed.
The 2% negative-split column runs 8:40 per mile to halfway, which it passes in 1:53:38, then 8:30 per mile. The first-half miles are only 5 seconds slower than goal pace, so the plan mostly asks you not to bank time early: its 10K check is 53:52 rather than 53:19.
By Riegel's formula a 3:45:00 marathon is level with a 1:47:55 half marathon and a 48:55 10K. If a recent race is well slower than that, the goal is a stretch; if it is well faster, a quicker goal may suit you better.