how to solve this depends a little bit on what your really want and what your functions look like, because in your example the solution is trival ... so can you elaborate on the problem??? (function? only 1 datapoint? estimate only 'a' and 'b' or the best fit with a,..,d??
if the function is linear and you have more datapoints (f and g?) you can run a regression. use left divide: \ or the command 'regress'
if the functions are more complicated than that, you can use 'fsolve'. which requires you to define a function, and an initial guess
