Question

plz help me !!!
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Answer 1

1. Since the number 21y5 is a multiple of 9.

So, the sum of its digits 2+1+y+5=8+y is a multiple of 9.

∴(8+y) is either 0 or 9 or 18 or ...

Since y is a digit, so (8+y) must be equal to 9.

i.e., 8+y=9

⇒y=9−8=1

2. Given that 31z5 is a multiple of 9.

According to the divisibility rule of 9, the sum of all the digits should be a multiple of 9.

Therefore,

3+1+z+5=9 OR 18

⇒z=9−9=0

⇒z=18−9=9

Answer 2

Refer the attachment !!!