In this problem, 25 is your constant (the number of baby hats you already started out with). 26 will be affected by your variable, d, the number of days. With each day that passes, 26 more hats will be knit, so the expression 26d can be used.
Set h equal to the constant + hats made per day to create an expression that you can use to solve for h: h = 26d + 25
Now, just plug the numbers in for d to get h: When d = 2, h = 26d + 25 = 26(2) + 25 = 77 When d = 4, h = 26d + 25 = 26(4) + 25 = 129 When d = 7, h = 26d + 25 = 26(7) + 25 = 207 When d = 9, h = 26d + 25 = 26(9) + 25 = 259