The graph shows the number of game systems sold
since 2015. Based on this information, which function best models the number of game systems sold in millions x years since 2015?
ア=21.35（0.7）*
ソニ30.5（21.35）*
ソニ30.5（1.3）*
y=30.5（0.7）*
It is difficult to determine the best function without having the actual graph or data points. However, based on the options provided, the best function that may model the number of game systems sold in millions x years since 2015 is:
y = 30.5(0.7)^x
This is because exponential functions of the form y = a(b)^x are commonly used to model population growth or decay over time. In this case, the base (0.7) represents the rate at which the number of game systems sold is decreasing, and the coefficient (30.5) represents the initial number of game systems sold in 2015.