If the simple interest is on $5,000 for 7 years is $1,400, then what is the interest rate

The right side of the equation is only a different way of writing the left side, so any value of x will solve this equation.

The equation   − 2 (  x  +  3  )  =  − 2 x  −  6  does not have any specific solutions for the simple reason that the left and rigth sides are two representations of the same equation.

We have  − 2 (  x  +  3  )  means that each term inside the parenthesis should be multiplied with  − 2 , i.e.

− 2 (  x  +  3 )  =  − 2  ⋅  x  −  2  ⋅  (  +  3 )  =  − 2 x  −  6

Which is exactly what the right side says.

Any value of x will, therefore, fulfill this equation.