Let's say David's age right now is x years
x + 6 = 2(x - 7)
x + 6 = 2x - 14
x = 20
Therefor David is 20 years old
The third one
U solve from left to right and when two negatives are next to each other it turns to a plus.
Answer:
the answer is 168
Step-by-step explanation:
you multiply with by length and you get 168.
1.) 1+10a-5a
Subtract 5a from 10a
Final Answer: 1+5a
3.) x-9-3x
Subtract 3x from x
Final Answer: -9-2x
5.) 1-4n+2n-1
Subtract 1 from 1
-4n+2n
Add
Final Answer: -2n
7.) 10k-3k
Subtract
Final Answer: 7k
9.) 5r+4-4
Subtract
Final Answer: 5r