D is a notation for differential. There is a d2 in your formula because in the numerator there are two differentials. The formula is thus the second derivative of a function with respect to two variables.
Answer:
63 in.3 that's what I got so I hope it's right
(2x+4)+(4x+2)+(2x-1)=180
8x+5=180°
8x=180-5
8x=175
X=21.875
A= 2(21.875)+4=47.75
B=4(21.875)+2 =89.5
C=2(21.875)-1=42.75
Do this and then simplify the result
Factorized: (a + b + 2) ^2