Question 1056875
 Let 
    n = number sold at $2 each
    k = number sold at $3 each

    Two unknowns, so we're looking for two equations

    n + k = 40        (Dave sold 40 tickets)
    2n + 3k = 88    (He collected $88)

     From the top eqn, k = 40-n, substitute this for k in the bottom eqn:

       2n + 3(40- n) = 88
       2n + 120 - 3n = 88
        -n =  -32
          n  = 32     (sold 32 tickets at $2 each)
          k = 8        (sold 8 tickets at $3 each)

Check:   8*3 + 32*2 =  24 + 64 = 88   (ok)