Answer:
84
Step-by-step explanation:
Let the first digit = x
Let the second digit =y
x + y = 12
x + 4 = 3*y
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From the second equation, we learn that x = 3y - 4
Put that into the first equation.
3y - 4 + y = 12 Combine the left side
4y - 4 = 12 Add 4 to both sides
4y = 16 Divide by 4
4y/4 = 16/4
y = 4
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x + 4 = 12
x + 4 - 4 = 12-4
x = 8
So the number is 84
