Is the set of multiples of 4 closed under addition? explain why or provide a counterexample if not.

a. yes, because the sum of any two multiples of 4 is also a multiple of 4.

b. yes, because the sum of any two multiples of 4 is also a multiple of 8.

c. no, and a counterexample is –4 + (–8) = –12.

d. no, and a counterexample is 26 + 16 = 42.

answer: bea's uncle is 25 years old.

step-by-step explanation:

given the equation , we can say that the variable "x" represents the age of bea's uncle. then to find his age, we need to solve for "x":

we must add 15 to both sides of the equation:

now we need to divide both sides of the equation by 3:

therefore, we can conclude that bea's uncle is 25 years old.