Alina started her stamp collection with 15 stamps. every month after that, she added 3 more stamps to her collection how many stamps did alina have in her collection after 36 months?

123

Step-by-step explanation:

15 + 3 (36) = 123

it's equivalent, so we can say that its equal.

let's call the denominator x and the numerador is 18 less then denominator, x - 18.

multiply

2.x = 5.(x - 18)

2x = 5x - 90

90 = 5x - 2x

90 = 3x

x = 90/3

x = 30

so: