$$18\times[7+(-3)]=[18\times7]+[18\times(-3)]; (-21)\times[(-4)+(-6)]=[(-21)\times(-4)]+[(-21)\times(-6)]$$
$\text{true}$
$$18\times 4=18\times 7+18\left(-3\right)\text{ and }-21\left(-4-6\right)=-21\left(-4\right)-21\left(-6\right)$$
$$72=18\times 7+18\left(-3\right)\text{ and }-21\left(-4-6\right)=-21\left(-4\right)-21\left(-6\right)$$
$$72=126-54\text{ and }-21\left(-4-6\right)=-21\left(-4\right)-21\left(-6\right)$$
$$72=72\text{ and }-21\left(-4-6\right)=-21\left(-4\right)-21\left(-6\right)$$
$$\text{true}\text{ and }-21\left(-4-6\right)=-21\left(-4\right)-21\left(-6\right)$$
$$\text{true}\text{ and }-21\left(-10\right)=-21\left(-4\right)-21\left(-6\right)$$
$$\text{true}\text{ and }210=-21\left(-4\right)-21\left(-6\right)$$
$$\text{true}\text{ and }210=84+126$$
$$\text{true}\text{ and }210=210$$
$$\text{true}\text{ and }\text{true}$$
$$\text{true}$$
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