In the following reaction:

The major product $A$ is:

The reaction proceeds via a carbocation intermediate:Protonation of the double bond:
$${\text{(CH}}_3{)}_3\text{C}-\text{CH}={\text{CH}}_2+{\text{H}}^{+}\to {\text{(CH}}_3{)}_3\text{C}-{\text{CH}}^{+}-{\text{CH}}_3\text{ (Secondary carbocation)}$$
A $1,2\text{-methyl shift}$ occurs to form a more stable tertiary carbocation:
$${\text{(CH}}_3{)}_3\text{C}-{\text{CH}}^{+}-{\text{CH}}_3\stackrel{1,2-\text{methyl shift}}{\to }{\text{(CH}}_3{)}_2{\text{C}}^{+}-{\text{CH(CH}}_3{)}_2\text{ (Tertiary carbocation)}$$
Nucleophilic attack by ${\text{H}}_2\text{O}$ and loss of ${\text{H}}^{+}$:
$${\text{(CH}}_3{)}_2{\text{C}}^{+}-{\text{CH(CH}}_3{)}_2+{\text{H}}_2\text{O}\to {\text{(CH}}_3{)}_2\text{C(OH)}-{\text{CH(CH}}_3{)}_2$$
The major product is $2\text{-methyl-2-butanol}$ substituted with isopropyl, specifically $2,3\text{-dimethyl-2-butanol}$.