7/10n + 14 = 49
7/10n = 35
n = 35 x 10/7
n = 50
90*4-14/2+102/5*2
360-7+40,8
393,8
The third option is ordered least to greatest
I've attached a plot of one such cross-section (orange) over the region in the x-y plane (blue), including the bounding curves (red). (I've set

for this example.)
The length of each cross section (the side lying in the base) has length determined by the horizontal distance

between the y-axis

and the curve

. In terms of

, this distance is

. The height of each cross section is twice the value of

, so the area of each rectangular cross section should be

.
This means the volume would be given by the integral
Well, to add fractions, you need to find a common denominator. In this case, the smallest common denominator would be 12. So you must multiply each fraction so that both denominators are 12.
3/4*3/3=9/12
1/3*4/4=4/12
Add those two fractions together, reduce if possible, and you have your answer!
9/12+4/12=13/12
You can't reduce, so 13/12 is your answer.
Hope it helps!
-Lacy