Hello there!
To solve for the variable of d, the first thing you must do is to subtract over any constants in order to isolate the term with the variable in it.
In this case, you would subtract 85 from both sides:
7.5d+85-85=130-85
When this simplifies, you should get:
7.5d=45
Now, divide both sides by 7.5 to isolate d:
7.5d/7.5=45/7.5
This would result in your answer, d=6
To check if this is correct, plug 6 back into the original equation to see if you result in 130=130:
7.5(6)+85=130
45+85=130
130=130
Hope this helps!