Let numbers be x at ones place and y at tens place so
10y+x is that digit
now reversed digit is 10x+y
according to question
7 (10y+x)=4(10x+y)
x=2y........... (i)
now,
given x-y=3
from eq. (i) 2y=x
2y-y=3
y=3
so,
x=63
required original no. is 36 and reversed digit is 63