Zachary purchased a computer for 1800 on a payment plan. three months after he purchased the computer, his balance was 1350. five months after he purchased the computer, his balance was 1050. what is an equation that models the balance b after m months

1800 - 1350= 450 3 months after the purchase he payed $450
450/3= $150 per month

1350 - 1050= 300 5 months AFTER THE PURCHASE he payed $300
300/2= $150 per month
^after 2 more months he payed $300^

$150 per months

Equation: (initial amount) - (150)M
M= amount of months after purchase

B = 1800 - 150M

The answer would be -3.9> -4.5