Answer
$\Delta H = +90kJ$
Work Step by Step
The Hess's law states that, if a reaction have two or more steps, like the one in the problem:
$A --> B$ $ :\Delta H = + 30kJ$
$B --> C $ $ : \Delta H = +60kJ$
The entropy can be calculated by the sum of the two steps involved.
$\Delta H : A --> C = (+30kJ) + (+60kJ) = +90kJ$
