7. (15 points) The rules of a "fun game" are as follows: The player has four skills: Water, Fire, Wind, and Earth. Each skill requires a certain number of crystals to activate, and the specific effects of each skill are as follows:
Water: Consumes 4 crystals, and simultaneously reduces the enemy's health by 4 points (if the enemy's health is less than 4 points, it is directly killed); Fire: Consumes 10 crystals, and simultaneously reduces the enemy's health by 11 points (if the enemy's health is less than 11 points, it is directly killed); Wind: Consumes 10 crystals, and simultaneously reduces the enemy's health by 5 points (if the enemy's health is less than 5 points, it is directly killed) and the next skill's crystal consumption is halved (for example: if the Water skill is used after the Wind skill, the Water skill only consumes 2 crystals);
Earth: Consumes 18 crystals, and simultaneously halves the enemy's health (if the enemy's health is odd, add 1 first and then divide by 2): If the enemy's health is 120 points, then by reasonably selecting skills, at least $\qquad$ crystals are needed to kill the enemy (the enemy is killed when its health is reduced to 0).
【Solution】Solution: Observing, using Wind first and then Earth can consume fewer crystals. The following method uses the least (as shown in the table),

Only 63 crystals are needed,
\begin{tabular}{|c|c|c|}
\hline Skill & Crystals Needed (each) & Enemy Remaining HP (points) \\
\hline Wind & 10 & 115 \\
\hline Earth & 9 & 58 \\
\hline Wind & 10 & 53 \\
\hline Earth & 9 & 27 \\
\hline Wind & 10 & 22 \\
\hline Fire & 5 & 11 \\
\hline Fire & 10 & 0 \\
\hline
\end{tabular}
Therefore, the answer is 63.