Answer:
60
Explanation:
First set up your equation
All triangles have angles that add up to 180, this means that you can make an equation where all your sides = 180
here is the equation: 7x-3+9x-1+40= 180 (i just wrote all the sides we can see)
Then you'll want to solve for x
7x-3+9x-1+40= 180
first combine like terms. We have a 7x and a 9x, so add them together
This will give you 16x-3-1+40=180
Now since your plain numbers (no variable) are on the same side of the = sign, you can just deal with them now. You can do -3-1+40 which is 36.
Now you have 16x+36=180
Now you'll want to take 36 from both sides. 36 is positive right now so you should do the opposite and subtract it from both 180, and itself.
This leaves you with: 16x=144
You have 16x which is the same as 16 times x. You want to do the opposite again. The opposite of multiplying is dividing so divide 144 by 16. This gives you 9 which is your x value.
Now one last thing. to get A on the triangle you can plug your X value (9) into the equation it gave you (7x-3)
this looks like 7(9)-3. 7 times 9 is 63. 63 -3 is 60.
(you can check your answer by plugging 9 into the other equation and adding everything up. it will equal 180)