We need to form and solve a system of linear equations to find the individual cost of one pencil and one pen. Calculation: Let the cost of one pencil be x and the cost of one pen be y . We have the equations: ⇒21x+9y=276 ⇒6x+3y=84 Divide equation (2) by 3 : ⇒2x+y=28 Multiply equation (3) by 9 : ⇒18x+9y=252 Subtract equation (4) from equation (1): ⇒(21x+9y)−(18x+9y)=276−252 ⇒3x=24 ⇒x=8 Substitute x=8 into equation (3): ⇒2(8)+y=28 ⇒16+y=28 ⇒y=12 Hence, the cost of one pencil and one pen is: ⇒x+y=8+12 ⇒x+y=20