Final answer:
The seasonal index for the first quarter is 74.67.
Step-by-step explanation:
To find the seasonal index for the first quarter, we need to calculate the average sales for all quarters and then divide the sales of the first quarter by that average.
Average sales = (140 + 225 + 255 + 130) / 4 = 187.5
Seasonal index for the first quarter = (Sales in the first quarter / Average sales) * 100 = (140 / 187.5) * 100 = 74.67