Question 973858
x= number of hits needed,  Each hit equals an at bat.  

(45+x)/(130+x) =0.4
multiply  both sides by (130+x)
45+x=52+ 0.4 x
0.6 x=7; divide by 0.6.

x=12 (11.667)
check 57/142 (12 hits) 0.401
56/141 (11 hits)  0.397

So 12 hits are necessary, since there are no fractions of hits.