1500 - [ 820 - 16 x ( 125 x a - 150 ) :80 ] = 700
1500 - [ 820 - 16 x 5 (25 x a - 30 ) : 80 ] = 700
1500 - [ 820 - 80 (25 x a - 30 ) : 80 ] = 700
1500 - [ 820 - 25 x a + 30 ] = 700
1500 - [ 850 - 25 x a ] = 700
1500 - 850 + 25 x a = 700
25 x a = 50
a = 2