$\left( 30+9 \right) \times 2=30 \times 2+x \times 2$
Multiply the numbers$\left( 30+9 \right) \times 2=60+x \times 2$
Use the commutative property to reorder the terms$\left( 30+9 \right) \times 2=60+2x$
Add the numbers$39 \times 2=60+2x$
Multiply the numbers$78=60+2x$
Move the variable to the left-hand side and change its sign$78-2x=60$
Move the constant to the right-hand side and change its sign$-2x=60-78$
Calculate the difference$-2x=-18$
Divide both sides of the equation by $-2$$x=9$