How many carbon atoms are in the following molecule of isobutane? (ch3) 3ch

The subscript 3 outside of the parentheses means to multiply everything in the parentheses by 3, so it becomes a matter of addition:

3 * (CH3) * (1 carbon atom) / (CH3) = 3 carbon atoms in (CH3) 3

CH has one carbon atom and one hydrogen atom, so:

1 carbon atom in CH

Add both of them together, and you get 4 carbon atoms in isobutane