Please Help! I will give you the brainiest and a lot of points!

Arley is building a model of a city map. in one part of the city, three roads form a right triangle, which harley draws as triangle abc, with the following measures: m∠b=90° and m∠a=30°. in his scale model, the hypotenuse of triangle abc, ac¯¯¯¯¯¯¯¯, has a length of 817−−√ cm. what is the value of a (the length of bc¯¯¯¯¯¯¯¯)?

Given f(x)= 9x+1 and g(x)=x^3, choose the expression (f*g)(x)

Using only the digits 5, 6, 7, 8, how many different three digit numbers can be formed if no digit is repeated in a number?