] =(x+11)⋅1+(2x+13)⋅1+(3x+15)⋅x ⇒(x+11)+(2x+13)+(3x2+15x) ⇒(3x2+18x+24) Equate the result to 45 : (3x2+18x+24=45)
⇒(3x2+18x−21=0) (x2+6x−7=0) (x2+7x−x−7=0) ⇒(x=1 or x=−7) Step 5: Verify: For X=1, substitute back: (3(1)2+18(1)+24=45) 45=45 ∴ The correct value of x is 1 .