The correct answer is D.
A function cannot have an x-value that corresponds to more than one y-value.
In this table, the x-value '8' corresponds to two separate y-values; 8 and 5, making it invalid as a function.
        
             
        
        
        
1. Angles ADC and CDB are supplementary, thus
m∠ADC+m∠CDB=180°.
Since m∠ADC=115°, you have that m∠CDB=180°-115°=65°.
2. Triangle BCD is isosceles triangle, because it has two congruent sides CB and CD. The base of this triangle is segment BD. Angles that are adjacent to the base of isosceles triangle are congruent, then
m∠CDB=m∠CBD=65°.
The sum of the measures of interior angles of triangle is 180°, therefore,
m∠CDB+m∠CBD+m∠BCD=180° and
m∠BCD=180°-65°-65°=50°.
3. Triangle ABC is isosceles, with base BC. Then
m∠ABC=m∠ACB.
From the previous you have that m∠ABC=65° (angle ABC is exactly angle CBD). So 
m∠ACB=65°.
4. Angles BCD and DCA together form angle ACB. This gives you
m∠ACB=m∠ACD+m∠BCD,
m∠ACD=65°-50°=15°.
Answer: 15°.
 
        
                    
             
        
        
        
Answer:
She is right, it won´t always work.
Step-by-step explanation:
Hi, in the examples this tactic works because the first numbers, when multiplied, don´t equal 10 (7x6=42 and 8x7=56). If you multiply both numbers and give you 10, you will have to add another zero to the final number and the trick would crash.
Example:
     200    x       500      =    100,000
(2 Zeros)      (2 zeros)        (5 zeros)
Best of luck.