Step-by-step explanation:

- In the line 2, only variables were operated with a reduction of similar terms in each side of the equation, giving as result -4x at one side, and 2x at the other side.
- In the line 3, terms with variables were joined together in one side of the equation, and then, they were operate it, given as result -6X.
O=4i (is that was you were asking about)
edit: sorry that wasn't very detailed say if the input is 4 the output will be 16 or if the input is 100 the output will be 400. So mainly what ever the input is multiply it by 4.
I hope this helps :)
The answers is 2 x 3 x 6 = 36
21-7=14 is a relate subtraction problem
19 hundreds. 19 time 100 is 1900