1.76-[16-3.2{1.3+(6.43-3.75÷1.2)}] is solved by calculating the contents of each bracket starting with the innermost.
6.43-3.75÷1.2. Division has to be done before subtraction: 6.430-3.125=3.305. Remember this value.
Next brackets: 1.3+3.305=4.605. Remember this value for the next step.
Next brackets: 16-3.2*4.605. Multiplication takes priority over subtraction: 16-14.736=1.264.
Finally: 1.760-1.264=0.496.