Answer
$$11y^3-9y-1.2$$
Work Step by Step
Recall, like terms must (1) be raised to the same power and (2) consist of the same variable (i.e. x and y are not like terms). It is also important to note that numbers are all like terms with each other when not multiplied by anything. Doing this, we find:
$$1.4y^3+9.6y^3-7.7y-1.3y+2.9-4.1\\ 11y^3-9y-1.2$$
