justify means plug answer in and verify
so distribute 8(3-7x)=24-56x
143=7+24-56x
143=31-56x
minus 31 both sides
112=-56x
divide both sides by -56
-2=x
justify
plug it back
143=7+8(3-7x)
143=7+8(3-7(-2))
143=7+8(3-(-14))
143=7+8(3+14)
143=7+8(17)
143=7+136
143=143
true
x=-2