Here, in the second line, there are plus signs (+'s), indicating this is addition. But this time, unlike the first line, the numbers are grouped together with parentheses. When numbers are grouped with parentheses, it means it is the Associative property. Because we are adding, it's the associative property of ADDITION.
B. “Y = 15x” would be your answer. Y is your end balance and x is the weeks. For example, if x is 3 weeks, your equation would be 45 = 15*3. In this case, y would be 45. Need anymore help?
In the 10^4 can be written as 10 exponents 4, which is not equal to 40,000. Tia's opinion was incorrect because the exponential shows how much they multiply that base number.