Let x represents the number of months it will take Kelsey to have more money than Kyle.
Given that Kelsey starts with $150 in her account and she adds $25 a month, it means that the amount that he would have saved after x months is
150 + 25 *x
= 150 + 25x
Given that Kyle starts with $200 in his account and adds $20 a month to his account, it means that the amount that he would have saved after x months is
200 + 20 *x
= 200 + 20x
For Kelsey to have more money than Kyle, the inequality would be
150 + 25x > 200 + 20x
25x - 20x > 200 - 150
5x > 50