This is a quadratic equation. There's a shortcut (two shortcuts really) called the Shakespeare Quadratic Formula (2b or -2b) applicable when the middle term is even:
OK, our problem is
Typically we'd write 
but the answers here don't so we won't either.
Answer: C and D
All Triangles are equilateral ( each side = 4)
Area of a Triangle is (B x H)/2. B being the base ( 4) & H the altitude.
WE know that altitude in an equilateral triangle, H = ( side x√3)/2
So H= (4√3)/2 = 2√3
The area of one triangle = (4 x 2√3)/2 = 4√3
And for the 3 triangles the lateral area = (4√3) x 3 = 12√3
If 9 chairs were sold, the store has to sell 11 tables in order to meet the requirements.
The answer is 10,5 i think
