If

21 = 42

39 = 618

17 = 214

then what does

45 = ?

810

Step-by-step explanation:

21 = 42

Decode:

Number in the tens place = 2 x 2 = 4

Number in the ones place = 1 x 2 = 2

Answer: 42

39 = 618

Decode:

Number in the tens place = 3 x 2 = 6

Number in the ones place = 9 x 2 = 18

Answer: 618

17 = 214

Decode:

Number in the tens place = 1 x 2 = 2

Number in the ones place = 7 x 2 = 14

Answer: 214

Find 45

Number in the tens place = 4 x 2 = 8

Number in the ones place = 5 x 2 = 10

Answer: 810