I need help on calculating block

I have Legacy Saffell's Frame 111% & corrupted 3% spell block stone of lazwhar, I also want to use acrobatics, but I don't know how many block nodes I need to get a cap 75% spell block with acrobatics

X * 0.7 = 75%
X = 107%

So to cap spell block, you need to have 107% spell block before acrobatics.
Seeing as you are converting 161% of block to spell block you need:

(107 - 3 [lazhwar flat]) / 1.61 = 65% block chance total

Given saffel gives 24% you need another 41% block chance from the tree, which isn't possible without BoR afaik.

Edit:

If you grab the 7% spell block from witch you need:

(107 - 10) / 1.61 = 60% block chance total

So you only need 36% block chance from the tree.

If you use rainbow strides, without witch nodes:

(107 - 3) / 1.86 = 56% block chance total

-24% saffel = 32% block chance needed from tree

And if you grab both rainbowstrides + witch spell block nodes:

(107 - 10) / 1.86 = 52% block chance total

-24% saffel = 28% block chance needed from tree / other items.

thank you