Right heres a Q on the heat equation that should be simple but im making a mistake somewhere.....

Since I wasn't entirely sure what to do i figured if i sub in the values of a and b into the exponential then differentiate with respect to and again but twice with respect to x then both answers should be equal.

but for i got

and for i got

have i made a mistake somewhere or should i have subbed into the Black-Scholes equation (in which case i think ill leave this Q alone for now...)