79x68+[1400-(777-687x5)]x4=

79x68+[1400-(777-687x5)]x4=79x68+[1400-(777-3435)]*4=79x68+[1400-(-2658)] *4=5372+[1400+2658]*4=5372+4058*4=5372+16232=21604

5372 + [ 1400 + 2658 ] x 4 =  21604   Proszę ;)