LET THE DIGIT AT TEN" S PLACE BE X & UNIT"S PLACE BE Y
REQ. ORIGINAL NO. = 10X+Y
REVERSED NO. =10Y+X
ALSO Y - X = 3 => Y = 3 +X
A/Q, 7(10X+Y) = 4 (10Y+X)
=> 7( 11X + 3) = 4( 30 +11X)
=>77X -44X = 120 -21
=> 33 X =99
=> X = 3 & Y= 3 +X = 3 +3 = 6
REQ. ORIGINAL NO.=10X+Y = (10 × 3 ) +6 = 36