How do adjectives change form to become adverbs?

Many adjectives can become adverbs by adding the suffix -LY. For adjectives ending in LL, only a Y may be added.

Examples:

He felt helpless. He looked on helplessly.

The forecast was accurate. It had been accurately prepared.

The table was solid. It had been solidly built.

The table was full. The table was fully occupied.

His mind felt dull. He was only dully aware of his surroundings.