30%=0.3
3/8 * m = 0.3(m+10)
3/8 *m=0.3m+3
3/8 *m - 0.3 m =3
(3/8-3/10) * m =3
(15/40-12/40) * m = 3
3/40 * m = 3
m= 3:3/40
m=3 * 40/3
m=40
