Solve the following equation by using the addition principle. Check the solution. \( 13=\mathrm{a}-7.1 \) The solution is \( a=\square \). (Type an integer or a decimal.)

To solve the equation \( 13 = \mathrm{a} - 7.1 \) using the addition principle, we need to isolate \( a \). We can do this by adding \( 7.1 \) to both sides of the equation: \[ 13 + 7.1 = \mathrm{a} - 7.1 + 7.1 \] This simplifies to: \[ 20.1 = \mathrm{a} \] So, the solution is \( a = 20.1 \). Now, let's check the solution by substituting \( a \) back into the original equation: \[ 13 = 20.1 - 7.1 \] Calculating the right side gives: \[ 20.1 - 7.1 = 13 \] Since both sides of the equation are equal, our solution \( a = 20.1 \) is correct.