The equation given in the question is
13 + (w/7) = - 18
(91 + w) / 7 = - 18
91 + w = - 126
w = - 126 - 91
= - 217
I hope that the procedure is clear enough for you to understand. I also hope that this is the answer that you were looking for and the answer has actually come to your desired help.
Yes it is. Input the numbers into the pythagorean theorem,

and if they equal each other it is a right triangle.
X/-3 = 12 + x
x = -36 - 3x
4x = 36
x= = 9
The number is 9.
You add all the sides together and divide by the number of side so in your case it would be 6 sides and you should get your perimeter i think thats how you do it i could be wrong
Answer: -2049. Explanation: Use PEMDAS to solve the equation (parenthesis, exponents, multiplication/division, and addition/subtraction). First multiply the numbers that are being multiplied. You should get 44 + 27 - 2100 - 20. Now start from the beginning, and either add or subtract. The answer is -2049.