Fun Riddles: Find the Missing Number in the Given Picture

Received this riddle on WhatsApp today, it seems very easy at the beginning but then the number 7 at the end of the riddle seems to be incorrect. The numbers below are arranged according to a certain rule. Once you have figured out the rule, find the missing number. The number 7 in the final

Fun With Numbers Riddle: Find the Missing Number

Don’t forget to have fun with numbers, with this riddle you can have some quality time with your friends and family. Below you will see a series of equations, where the operator is used differently. Find the usage of the operator in the first 3 equations and then find the missing number in the last