What is the length of side s of the square shown below?

When y’all answer can y’all explain too !

Prove that the value of the expression 7^8–7^7+7^6 is divisible by 43.

Each person in an it department of 25 people works on at least one of 3 major projects: system security, program implementation, platform development. 10 people work on system security, 13 work on program implementation, and 12 work on platform development. 4 people work on system security and platform development, 5 people work on program implementation and platform development, and 2 people work on all three projects. how many people work on system security and program implementation?