How much part a and part b do j need to get npk of 3.1.1

that's a ratio for soil fertilizers. If in coco, probably using a soiless/hydro fertilizer solution? i'd shoot more for 1-1-2 NPK . My weighted average for vege (USA Label standards) N 7.73% P 6.19% K 13.41% Ca 6.47% Mg 4.47% S 6.00% You can see even "1-1-2" is heavily rounded, but close. Also the K-Ca-Mg ratio is 8-4-3 or so. "They" often say 4-2-1 for that one, i find marijuana needs more Mg than other flowering, soft-stemmed plants. These generalized ratios are not meant to be taken too literally. ballpark concepts at best. Observe and adjust. The plant dictates fine-tuning. Again, only good for a soilless/hydro context -- 100% plant-ready and 100% soluble fertilizers.

What does is the mix ratio on the packaging... They know better than us.

you cant hit exactly 3-1-1, the 2nd part is .3-4-3 Use the feed chat they provide. https://www.hornethydroponics.co.uk/feed-schedule Closest you can get is 3.2-1.0-0.75 This is a ratio of 3x Part A & 1x Part B but again follow their feeding guide don't go off script till you know what you are doing.

1 gallon water = 30ml Part A, 21ml Part B. Will give you approx 3.1.1