regex to start a number with 5 and have 8 digits or start with 10 and have 10 digits

regex to start a number with 5 and have 8 digits or start with 10 and have 10 digits

I currently have 2 expressions separately, but wanted to combine into a single statement using or

1st --- /^[5]\d{7}$/ 2nd --- /^10\d{8}$/