Teacher, how to get Malik was 2u+1/2 n Nick was 3u+1/2 at first? I don’t understand...

Since in the end, all have same number of sweets.
Therefore each have 630÷3=210

Nick is the last person in the action.
Nick gave ¼ to Lisa.
Nick left ¾ = 210
Nick gave ¼ = 210÷3=70 to Lisa.

Lisa received 70 total 210.
Lisa before receive 210-70=140
Lisa gave ⅓ to Malik.
Lisa left ⅔ = 140
Lisa at 1st 3/3 = 210
Lisa gave Malik ⅓=70

Malik gave 1/7 to Nick.
Malik left 6/7 = 210
Total Malik 7/7 = 245
So, 1/7 = 35
Malik before receive 70 from Lisa = 245-70=175. (At 1st)

Nick at 1st = 630-175-210
=245.
Or
Nick before gave to Lisa = 210+70=280
Nick at first, before received 1/7=35 from Malik= 280-35 =245.

2u+½u is because i assumed in the end all have 3u.
I should assume in the end all have 6u since Malik gave 1/7 to Nick and left with 6/7.
Mean 1u =2
½u = 1

Ok,thank u so much!

For model .. i redraw and uploaded.

I forgot Malik left with 6/7, thanks teacher!