Hey there! So for this question, you are going to let sin theta=x (or whatever variable you like)

So we get:

7x^2-22x+3=0

Look familiar now? So we can apply the quadratic formula to find x.

x=(22+-(22^2-4(7)(3))^1/2)/14

We get:

x=1/7 and x=3

Now, we back-substitute and get

sin theta=1/7

sin theta=3

So solving for theta we get:

theta=0.1433475689053653575950742801566183260989392131334643 (thanks to wolfram alpha for all the digits)

and, for 3, it is a special case where we get an imaginary number which is better when put into polar but I have the standard form as well:

theta=

1.57079632679489661923132169163975144209858469968755291048747... -
1.76274717403908605046521864995958461805632065652327082150659... i
(result in radians)