Step 1 :
Factor out common factor $ \color{blue}{ y^2 } $:
$$ 6y^4+7ty^3-20t^2y^2 = y^2 ( 6y^2+7ty-20t^2 ) $$Step 2 :
$ 6y^2+7ty-20t^2 $ can be written as
$$ 6y^2+7ty-20t^2 = \left( -4t+3y \right) \left( 5t+2y \right)$$The explanation for this step cannot be generated.