Every morning sasha exercises for 20 minutes. she exercises k minutes every evening. next week she will double her exercise time at night. write an algebraic expression to show how long sasha will exercise each day next week.

If k=20 minutes
Each day Sasha will exercise 2 times more. 2 times more than k is 2k.
So first week Sasha will exercise k+2k+3k+4k+5k+6k=20+40+60+80+100+120=440 minutes
The formula to show how long Sasha will exercise each day next week is:
440 + 20*x
where 440 is initial exercise time, and x is number of day in next week.