Simple Algebraic Equations Question 4

If $6 \cdot 2k = 72$, what is the value of $2k-4$?

$6$

$8$

$10$

$12$

Approach 1

Solve for $k$. $$6 \cdot 2k = 72 $$ $$ 2k=12 $$ $$ k=6 $$ Substitute our value of $k$ into the expression $2k-4$. $$ 2k-4$$ $$2(6)-4$$ $$12-4$$ $$8$$

Approach 2

We can reduce the number of steps by recognizing that $2k$ is present in the initial equation and final expression. $$6 \cdot 2k = 72 $$ $$ 2k=12 $$ Subtract 4 from both sides. $$2k-4=12-4$$ $$2k-4=8$$