The expression for how long Greg spent reading and writing during the challenge is y = 30x + 750.
For the initial 10 days, Greg read for x minutes and wrote for 15 minutes.
Therefore, for the 10 days, the expression for the days he read and write in the journal are:
= 10 × ( x + 15 minutes )
= 10x + 150 minutes
For the last 20 days, Greg read for x minutes and wrote for 30 minutes.
Therefore, the expression for the minutes he read and write in the journal in those 20 days is:
= 20 × ( x + 30 )
= 20x + 600 minutes
So, the expression for the number of minutes Greg read and write in his journal will be:
y = 10x + 150 + 20x + 600
y = 30x + 750
Learn more about expression here:
https://brainly.com/question/1718606
#SPJ9