Given: There will be 20 total angelfish, swordtails, and tetras.

a+s+t=20

Subtract {a}, {s} from each side.

t = 20-a-s

b) Given {problem a}, find total cost in dollars {C} when angelfish are $5, swordtails are $2, and tetra are $3.

C = 5a + 2s + 3t

Substitue given value of {t}.

C = 5a + 2s + 3(20-a-s)

Distributive property of multiplication & Defintion of subtraction

C = 5a + 2s + 60 + -3a + -3s

Associative Property of addition

C = 60 + (5a + -3a) + (2s-3s)

Combine like terms

C = 60 + 2a – s

C) Given {problem B} and a=4, s=10

C= 60 + (2*4) – 10

C = 60 + 8 – 10

C = $58

Check answer using a different method:

4@$5 + 10@$2, And the remainder of the 20 (6)@ $3.

20 + 20 + 18 = $58 Answer is correct.