Answer: 7
Step-by-step explanation: Cross multiply, so 15 times x and 21 times 5. 21 times 5 is 105 then you divide by 15 which gives you 7.
Answer:
C.2:4
Step-by-step explanation:
1*2=2
3*2=6
2:6=2:4
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not true so it is C.
Answer: 
Step-by-step explanation:
The formula for finding the nth term of an arithmetic sequence is given as:

first term = -15
common difference = -6 - (-15) = 9
number of terms
substituting into the formula , we have :

