What does this get?
csc 3.9076

-1.44245333364                

So, the relationship with i hours as the indecent variables would be  

Serena can't paint 400 square feet of wall space of wall space in 3.5 hours.

Step-by-step explanation:

Since we have given that

Area that she can paint = 60 square feet

Time taken = half hour = 30 minutes = 0.5 hours

Using "Unitary method, we get that

In 0.5 hours, she can paint = 60 square feet

In 1 hour, she can paint =  

In i hours, she can paint =  

Let the total area she can paint be 'y'.

So, the relationship with i hours as the indecent variables would be

Now,  Can Serena paint 400 square feet of wall space i. 3.5 hours

We put y = 400 and i = 3.5 hours to check whether it is equal or not.

Hence, Serena can't paint 400 square feet of wall space of wall space in 3.5 hours.