let Andrew's money is A, Barbara's money is B, the price of 1 comic book is q

Andrew did not bring enough money; in fact, to be able to buy that 1 comic book, he needs an additional $28.=> q= A+28 => A= q - 28
Meanwhile, Barbara did not bring enough money either; in fact, to be able to buy that 1 comic book, she needs an additional $26 => q= B +26 => B= q-26
=> A+B= q-28+q-26 => A+B = 2q - 54 (1)
if Andrew and Barbara combine their money; they will have enough to buy that comic book and still have $2 left.=> A+ B= q+2 (2)
From (1) and (2)=> 2q-54=q+2 => q= 56
So  the comic book costs 56