Pls help I’ll brainlest ASAP

I’m stuck on this i don’t understand.

Frank has a devised a formula for his catering business that calculates the number of meatballs he needs to prepare. the formula is m=4a+2c, where c=number of children; m=number of meatballs; a=number of adults. how many meatballs are required for a party of 10 adults and 5 children?

Consider the sequence below. 3 , 1 , 1/3 , 1/9 , select the explicit function which defines the sequence.