Evaluate: (8y^3+4y^2-5y+12)-(3y^2-6y-18)

Expression: $\left( 8{y}^{3}+4{y}^{2}-5y+12 \right)-\left( 3{y}^{2}-6y-18 \right)$

Remove unnecessary parentheses

$8{y}^{3}+4{y}^{2}-5y+12-\left( 3{y}^{2}-6y-18 \right)$

When there is a $-$ in front of an expression in parentheses, change the sign of each term of the expression and remove the parentheses

$8{y}^{3}+4{y}^{2}-5y+12-3{y}^{2}+6y+18$

Collect like terms

$8{y}^{3}+{y}^{2}-5y+12+6y+18$

Collect like terms

$8{y}^{3}+{y}^{2}+y+12+18$

Add the numbers

$8{y}^{3}+{y}^{2}+y+30$