X+3y=12 and y=6x+21 system of substitution

(x, y) = (- 3, 3)

Step-by-step explanation:

given the 2 equations

- x + 3y = 12 → (1)

y = 6x + 21 → (2)

Substitute y = 6x + 21 into (1)

- x + 3(6x + 21) = 12 ← distribute

- x + 18x + 63 = 12

17x + 63 = 12 ( subtract 63 from both sides )

17x = - 51 ( divide both sides by 17 )

x = - 3

Substitute  x = - 3 into (2) for y

y = (6 × - 3 ) + 21 = - 18 + 21 = 3

solution is (- 3, 3 )

4 pencils

Step-by-step explanation:

Note=  pencils costing 0. 90p

Given data

Balance= £10

pen= 3*1.45= £4.35

pencils=0.90p

change= £2.05

2.05= 10-4.35-90p

solve for p

2.05= 5.65-90p

collect like terms

5.65-2.05= 0.90p

3.6=90p

divide both sides by 90

p=3.6/0.90

p=4