So the question states: 'To convert degrees Celsius to Kelvin, the formula $K = C + 273.15$ is used. Solve this formula for $C$.'
The answer I came up with was: $K - 273.15 = C$. So is this correct? If so why not and how do I solve it?
Question #2: 'The formula $C = 2\pi r$ is used to calculate the circumference of a circle. Solve this formula for $r$.'
Answer for #2: I am completely confused what I'm supposed to do. If you guys could explain this one to me that'd be great! Else I'll just ask my teacher tomorrow.
Solving for a variable means finding a value for that variable which satisfies the given equation. In your case, you have to find a number $r$ such that $C = 2\pi r$. Now if you multiply both sides of the equation by $\frac {1}{2\pi}$ you get $\frac {C}{2\pi}=\frac{2\pi r}{2\pi}= r$, so we can see that the equation uniquely determines the value of $r$. In general when you want to solve for a variable that is multiplying some non zero constant, you multiply both sides of the equality by the inverse of the constant.