(6x^3/3x^4)^2 = (2/x)^2 = 4/x^2
First combine like terms and put the expression in standard form. This expression is now in simplest form and cannot be simplified anymore.
3a + 10ab - 7a^2b - 10ab^2 + 12ab - (-4) + (-a^2b) - 5a
-10ab^2 - 8a^2b -2a + 24ab - (-4)
Hope this helps
ANSWER
The required angle is

EXPLANATION
Let the angle whose sine is

be

Then

We take the inverse sign of both sides to obtain,

We use our scientific calculator to evaluate and obtain,