Step-by-step explanation: D in this case would have to equal 0, because filling in "D" with any number, would make the sides unequal.
For example, let's say D = 1 and E = 3, the equation would say "1 - 3 = 2 * 1 - 3". Solving the sides, would leave "-2 = -1", which make it a false answer.
Now, let's say D = 0 and E = 3, the equation would say "0 - 3 = 2 * 0 - 3". Solving the sides, would leave "-3 = -3", which is true.
