Use Subtraction
1. Subtract
x+2y=7
3x-2y=-3
-------------
4x+0y=4 SIMPLIFY 4x=4
2. DIVIDE
4x=4
x=1
Substitute that into either of the original equations to get x=1, y=3
Answer:
A = 2, the number is 3221
Step-by-step explanation:
In order for the number to be divisible by 9, the sum of it's digit has to be divisible by 9.
In our case,
where k is an integer. the easiest way happens when k=1

Higher values of k will likely most work (with k=2 you get A to be a non-integer, which can't work since it's the digit of a number, and with higher values of K you're not getting a number in base 10.
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I’m sorry I can’t help ypu