Base conversion and equations
Call the base "N". Then write the equation in base conversion form: The first one being:

4*N + 2 - 3 = 3*N + 6

Then solve for N

In general, digits in the second column (from the right) are multiplied by N, digits in the third column would be multiplied by \$N^2\$, digits in the fourth column would be multiplied by \$N^3\$, etc.