You need to follow the "order of operations", PEMDAS:
P = Parentheses
E = Exponents
M = Multiplications
D = Divisions
A = Additions
S = Subtractions
a) 5[3-8*3^2+4*6-2] (First we need to do all operations in the brackets (parentheses))
= 5[3-8*9+4*6-2] (Exponents 3^{2} = 9)
= 5[3-72+24-2] (Multiplications 8*9 = 72, 4*6=24)
= 5[3-96-2] (No divisions, so next is additions: 72+24=96)
= 5[-95] (Subtractions: 3-96 = -93, -93-2 = -95)
= -475 (Now multiply the 5 outside the bracket by the result (-95) inside the bracket)
b) Works the same as a) but involves a division. Do the numerator first, then the denominator, then divide the numerator by the denominator last.