Answer:
After 8 days they will have the same account balance of 460 dollars.
Explanation:
Let: x = total number of days
y = balance of dollars
y = mx + b → m = difference of dollars each day
b = initial amount of dollars
Therefore:
Michael → y = 30x + 220 ... [1]
Sally → y = -15x + 580.... [2]
------------------ (-)
0 = 45x - 360
x = 360 ÷ 45
= 8 days
y = 30x + 220
= 30(8) + 220
= $460