What would most likely happen if the amount of incoming solar energy decreased without a changed in the amount of reflection or outgoing radiation

Hi there, Alyssia!
The balance between incoming and outgoing radiation is known as radiation balance, and it's a critical process. If the balance was broken, in which less sunlight came and the amount of outgoing didn't change, it would most likely be a lot colder. If less heat is coming and we're letting it out at the same rate, temperatures would drop rapidly, perhaps leading to another ice age if it gets to a certain point.
Hopefully this helps!

3. is true i think i should be right