With a uniform electric field, flux go along parallel paths, then flux is therefore proportional to the cosine of the angle rotated. 0 degree rotation => cos(0)=1 => 100% of flux. 60 degrees rotation => cos(60) => 0.5 => how many % of flux?
The equation to find volume is V=r²h and you know all of your numbers other than h so you plug all that in. 100=3.14×2²×h → 100=3.14×4×h → 100=12.56×h → Divide 12.56 from both sides 100÷12.56=12.56×h÷12.56 → 7.96cm=h.