Question 319772
let the number be xy
x in tens place 
y in units place
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10x+y=7(x+y)-3
10x+y=7x+7y-3
3x-6y=-3
x-2y=-1.............. equation 1
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10y+x= 10x+y-18
9y-9x=-18
y-x=-2 ..............equation 2
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Add equation 1 & 2
x-2y+y-x=-1-2
-y=-3
y=3
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plug the value of y in equation 2
3-x=-2
-x=-5
x=5
the number is 53