In order to solve this SIMPLE problem. You need to know the INVERSE PROPERTY RULE. For example in this problem 8d=40 what is the 8 doing to the d? It’s multiplying it. And the OPPOSITE of multiplying is dividing. So in order to isolate the d you need to DIVIDE the 8 on both sides. Because WHATEVER you do on one side you must do to the other side. So far the equation should look like 8d/8=40/8. The 8d/8 gets canceled out. Leaving d=40/8. And finally that will be d=5.