What value makes 3(a+1.5)= -1.5 true

First, write the equation:
3(a+1.5) = -1.5
Next, you can distribute 3 into the parentheses by multiplying 3 by a and 1.5. It should look like this:
3a + 4.5 = -1.5
When trying to find the value of a variable, you want to get the variable to one side of the equation by itself. Subtract 4.5 from both sides of the equation to get:
3a = -6
Now, divide both sides by 3 to get your final
a= -2
The value that makes the equation true is -2
Hope this helped!

Element 17 is chlorine it is a group 7 element(halogen) and belongs to period 3 of the periodic table