Regarding your problem, the answer depends on the number of checks N.


"Ontario Trust" charges  8 + 0.5*N  dollars, where N is the number of checks.


"Maple Leaf Savings" charges  6 + 0.75*N  dollars.


Until

    8 + 0.5*N < 6 + 0.75*N,   (*)


"Ontario Trust" is cheaper.


You can easily solve inequality (*).

    8 - 6 < 0.75N - 0.5N

    2 < 0.25N  ====>  N >  = 8.


So, if the number of checks is greater than 8, the "Ontario Trust" is cheaper.


While the number of check is less than 8,  the "Maple Leaf Savings" is cheaper.


If N = 8,  then both banks charge the same.