Answer:
45 cm ( in my opinion)♀️
Explanation:
( Using the mirror formula)
1/ u + 1/v = 1/f
( introducing magnification; m into the formula )
u( 1/u + 1/v ) =u×1/f
1 + u/v =u/f
( But u/v =1 ÷v/u= 1/m)
1 +1/m =u/f
(Supposing m is actually equal to 2, and f =30 cm, then;)1 + 1/2 =u/30
2+1= u/15
3=u/15
3×15=u
45 cm=u