Problem 15

C₄H₉Br
Rule 1, replace halogens with hydrogens, gives C₄H₁₀
4 - 10/2 + 1 = 0 degrees of unsaturation.
No pi bonds and no rings.

The bands at 3000-2850 indicate C-H alkane stretches. The bands in the region 1300-1150 could indicate C-H wag (-CH₂Br) of an alkyl halide.

This is the structure. See if you can assign the peaks on your own.