7,2y+7,5=21,06

7,2у = 21,06 - 7,5

7,2у = 13,56

у = 13,56/7,2

у= 13  56/100 : 7  2/10 = 1356/100 : 72/10 =  1356/100 * 10/72 =13560/7200 =

=1  53/60

6,7×(35,712:4,8)+3,36 = 6,7 * 7,44 + 3,36 = 49,848 + 3,36 = 53,208