Bob spent twice as much as james, who spent four times as much as nava. if bob and james together spent $180, how much did james spend?

Let's say that Bob is x and James is y

x + y = 180
x = 2y

2y + y = 180
y = 60.
James spent 60 dollars. 

"Bob spent twice as much as James, who spent four times as much as Nava"

Bob:     b
James: j
Nava:   n

Bob spent twice as much as James:           b=2j
James spent four times as much as Nava: j=4n

Bob and James together spent $180:        b+j=180
but we have:                                                b=2j
                                                               
                                                                   2j+j=180
                                                                    3j=180      >>      j=60$
                                                                                               b=2j=120$
Recall this: j=4n >>>>    60=4n >>>>>n=15$

SO far we calculated how much everyone spent

I hope that helps!