1/10 is the next fraction in the sequence. If you multiply the numerator and denominator by a common factor to give each fraction a denominator of 20, the pattern goes 6/20, 5/20, 4/20, 3/20. The next term would be 2/20 which equals 1/10.
So it seems as if the first problem is asking this:

.
If x=0.15, then 11/15*(0.15) is 0.11 or 11/100.
The second problem is asking:

To solve algebraically, you want to get rid of the denominators under the x's. To do so, you want to multiply by the Least Common Multiple (LCM) of the denominators. For 3 and 4, the LCM is 12. Multiply everything by 12 to get:
3x+6=4x+2
Now, solve for x
Subtract 4x from both sides:
-x+6=2
Subtract 6 from both sides:
-x=-4
Multiply by -1 on both sides:
x=4.
It is x=8 because 13+7=20 and 28-20 would be 8 and that's the missing number.
Answer:
960vol cavalieri's principle applies
Step-by-step explanation:
8x6x20 for vol
"Cavalieri's Principle. If, in two solids of equal altitude, the sections made by planes parallel to and at the same distance from their respective bases are always equal, then the volumes of the two solids are equal "(Kern and Bland 1948)
both same height both equal in all ways