6sin^2 a - 11sin a + 4 = 0 , domain is from -360 until 360 degrees

we learned that, you need to isolate sin a, and then find the possible angles. I just need to know how to isolate sin a.

so i thought maybe this....

6 (sin a + sin a) - 11sin a = -4

but i dont know from here on....

please help!! exam is coming up!