Experts can i have the answer for the 15 th question (part c)

Dear Student,
Q15 (c)The order of stability of carbocation 
$C{H}_{3}C{H}_{2}C{H_2}^{+}\left(I\right)<\left(C{H}_3{)}_{2}CC{H_2}^{+}\right(II)<C{H}_{3}C{H}^{+}C{H}_{2}C{H}_3(III)<(C{H}_3{)}_3{C}^{+}\left(IV\right)$
The tertiary carbocations are more stable than secondary carbocations while secondary are more stable than primary.
The presence of alkyl group stabilizes the carbocation due to +I effect , the alkyl groups push the electron density towards the carbocation and the positive charge gets stabilized due to incoming negative from the alkyl group
Both I and II are primary carbocations but in case of II the there are 2 CH₃ groups while in I only one CH₃ group.
III is a 2⁰ carbocation  while III is most stable since it is 3⁰ carbocation.
Regards!