$\"\"$

The equation is $\"\"$ b $\"\"$ 15 = $\"\"$ 21.

Apply addition property of equality: If a = b then a + c = b + c.

$\"\"$ b $\"\"$ 15 + 15 = $\"\"$ 21 + 15 (Add 15 to each side)

$\"\"$ b = $\"\"$ 21 + 15 (Apply additive inverse property: $\"\"$ 15 + 15 = 0)

$\"\"$ b = $\"\"$ 6 (Add: $\"\"$ 21 + 15 = $\"\"$ 6)

Apply multiplication property of equality: If a = b then $\"\"$ .

$\"\"$ 1( $\"\"$ b) = $\"\"$ 1( $\"\"$ 6) (Multiply each side by negative one)

b = 6 (Product of two same signs is positive) $\"\"$

Check:

To check the solution, substitute b = 6 in original equation.

$\"\"$ b $\"\"$ 15 = $\"\"$ 21 $\"\"$ $\"\"$ 6 $\"\"$ 15 = $\"\"$ 21

$\"\"$ 21 = $\"\"$ 21 (Subtract: $\"\"$ 6 $\"\"$ 15 = $\"\"$ 21)

The statement is true. $\"\"$

The value of b = 6.