Hey there! I'm happy to help!
We see that Jack has already run 25 miles.
25
He also wants to run 2.5 miles every day. This means we will multiply 2.5 miles by the number of days he runs. We will call the number of days x.
25+2.5x
And he needs this to equal 275.
25+2.5=275
We subtract 25 from both sides.
2.5x=250
We divide both sides by 2.5
x=100
So, Jack will need to run 100 days to meet his goal.
Have a wonderful day and keep on learning! :D