①: 10+20+....+80=360 ?

2 10*2-360=60

(It is enough to allocate 60, so the middle allocation is determined to be 20,40. )

②:2 10-60= 150

(The remaining numbers are: 10, 30, 50, 60, 70, 80; As long as the sum of three numbers on one side is equal to 150)