Answer:
54
Explanation:
First write the list of numbers which the tens number is one less then ones place.(21,32,43,54,65,76,87,98). Remember this list then add the digits together. If you know your multiplication, the first 5 should be easy to solve so multiple the sum you received from adding the numbers by 6 until you get to one with the same starting number
(21)2+1= 3 x 6= 18
(32)3+2= 5 x 6= 30
(43)4+3= 7 x 6= 42
(54)5+4= 9 x 6= 54
(65)6+5=11
(76)7+6=13
(87)8+7= 15
(98)9+8 = 17
