We know that Kayla is level 12 and gains 6 levels everyday. We know that Maddy is level 28 and gains 2 levels everyday. To find which day they are both the same level we can add.
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Day 1:
Kayla is level 12
Maddy is level 28
Day 2:
Kayla is level 18 (12 + 6)
Maddy is level 30 (28 + 2)
Day 3:
Kayla is level 24 (18 + 6)
Maddy is level 32 (30 + 2)
Day 4:
Kayla is level 30 (24 + 6)
Maddy is level 34 (32 + 2)
Day 5:
Kayla is level 36 (30 + 6)
Maddy is level 36 (34 + 2)
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They willl be at the same level on level 36.
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Best of luck!