It is the Identity Property of Addition
The identity property of addition is that the sum of any number and its identity value gives the same number as the result. Also, 0 is the identity element.
Answer:
Diameter=60.79
Step-by-step explanation:

3/4 + 8/9
= (3*9)+(4*8) / (4*9)
= 27+32 / 36
= 59/36
= 1 23/36
X=7. 42/14=3. so x+5 times 3 = 7x-13. do the math, x =7. 7+5=12. 7(7)-13= 36. 12x3=36. boom.