Answer: 
Step-by-step explanation:
Given
It takes 20 min and 30 min for a person and his friend to paint a wall individually i.e.
In 1 min they cover
part and
part of wall respectively.
If the work together, 1 minute work is

Time required will be reciprocal of it

Answer:
The best way to know weather the formula y=x⁴-4x³+3x² is growing or not, is by graphing it.
As you can see in the attached picture:
- For -inf<x< 0 the graph decreases.
- For 0<x<0.634 the graph is growing
- For 0,634<x<2.366 the graph decreases
- For 2.366<x<+inf the graph is growing.
Therefore, the polynomial grows in the intervals stated before.