The most important thing to remember here is "order of operations" PEMDAS. parenthesis, exponents, multiplication, division, addition, subtraction.
start with parenthesis, (4/5) is equal to 0.8 and (17•2) is equal to 34.
so now rewrite it to be 4•0.8+6-34
4•0.8 equals 3.2
rewrite as 3.2+6-34
3.2+6 equals 9.2, subtract 34 you get -24.8