Solve 500*1*(87-90)+K(87-12)=0

$$500 \times 1 \times ( 87 - 90 ) + K ( 87 - 12 ) = 0$$

Solve for K

$$K=20$$

Steps for Solving Linear Equation

Multiply 500 and 1 to get 500.

$$500\left(87-90\right)+K\left(87-12\right)=0$$

Subtract 90 from 87 to get -3.

$$500\left(-3\right)+K\left(87-12\right)=0$$

Multiply 500 and -3 to get -1500.

$$-1500+K\left(87-12\right)=0$$

Subtract 12 from 87 to get 75.

$$-1500+K\times 75=0$$

Add 1500 to both sides. Anything plus zero gives itself.

$$K\times 75=1500$$

Divide both sides by 75.

$$K=\frac{1500}{75}$$

Divide 1500 by 75 to get 20.

$$K=20$$