1500 -[820-16×(125×a-150)÷80]=700
[820-16×(125×a-150)÷80] = 1 500-700
820-16×(125×a-150)÷80 = 800
16×(125×a-150)÷80 = 820-800
16×(125×a-150)÷80 = 20
16×(125×a-150) = 20×80
16×(125×a-150) = 1 600
125×a-150 = 1 600:16
125×a-150 = 100
125×a = 100+150
125×a = 250
a = 250:125
a = 2