What does the i after the sequence number in summation notation mean?

The "i" will be your starting point, from where you'll start adding the numbers.

Sigma notation or summation notation is a way used in mathematics, you might also call it a formula, used to shorty write systematical sums (that have a pattern in the summed digits).

→ The image below might be of great use and help.

Hope it helped,

BioTeacher101

b. 1.25 hr

step-by-step explanation:

if you have a constant speed of 60 mph, then you have a ratio between 60 mi. to 1 hr. dividing both sides by 60 we get the ratio

1 mi. to

then mult. both sides by 75 we get the ratio

75 mi. to

simplifying we get

75 mi. to

or 1.25 hr.