The angles number would be 230
0.0094% error
Divide 150/141. You get 0.94, then you need to find the percentage of that by clicking the percent button of your calculator
That questions answer depends on the size and composition of the horseshoe
By either long or synthetic division, it's easy to show that

The quartic will be exactly divisible by

when the numerator of the remainder term vanishes, or for those values of

such that

I'm not sure how to count the number of solutions (software tells me it should be 80), but hopefully this is a helpful push in the right direction.