remove all hyphens
check string length
if length < 10
error
else if length=10
make it 416-123-4567
else if length >10
make it 416-123-4567 ext 8999
check string length
if length < 10
error
else if length=10
make it 416-123-4567
else if length >10
make it 416-123-4567 ext 8999