This problem can be solved in two ways, the long way, or the short way.
1. The long way
We know that the base of the triangle is along the x-axis, and the length of the base is 20.
The centre of mass is located at 2/3 of the distance from vertex (3,4) along the median, which cuts the base at (10,0).
Therefore the centre of mass is located at
x=3+(10-3)*2/3=23/3
y=4/3
2. The short way
It turns out that the centre of mass of a triangle sheet is located at the mean of the coordinates of the three vertices, i.e.
CG=((0+20+3)/3, (0+0+4)/3)=(23/3, 4/3) as before.
I’m not 100% sure but isn’t it x2 +xy +y2?
They always try to trick you with this. Remember anything 5 or above would round up, anything 4 and under would round down. So look for the tenth place. that's the 9. The number to the right is 8 which is greater than 5. That means round up. You can't round it to 0.1 because that takes it back down. So you just move it over. The answer is 1.0.
During Distributive property, the number on the outside of the parenthesis basically gets multiplied by the numbers inside the parenthesis. In this case, you would multiply 6 by 5 and 4. When you get the products, then follow the sign that comes next. In this case, you would add the products to get a total sum. I attached a photo for further reference.
Hope this helps!