8n legs.

From the question, one crab has 8 legs, 2 crabs have 16 legs, number of legs = number of crabs × 8.

And there is 1 × 8 = 8, 2?× 8 = 16, so obviously the equation holds.

So the number of legs of n crabs is n? × 8 = 8n. i.e. n crabs 8n legs.

Extension:

Equation

Equation (equation) is Refers to an equation that contains an unknown number. It is a type of equation that expresses an equal relationship between two mathematical equations (e.g., two numbers, functions, quantities, operations), and the value of the unknown that makes the equation valid is called the "solution" or "root". The process of finding the solution to an equation is called "solving the equation".

Solving an equation eliminates the need to think backwards, and allows you to work forward to the equation containing the quantity you want to solve. Equations have many forms, such as quadratic equations, binary equations, quadratic equations, and so on, and can also form a system of equations to solve for multiple unknowns.