I've been trying to solve this equation and keep getting it wrong

Consider the function / (x) = x + 12x3 (3] Find the domain of f (I)- Note: Use the letter U for union. To enter co, type infinity with a lower case i. Domain: [-infinity, infinity) (b) Give the horizontal and vertical asymptotes of f (x ), if any. Enter the equations for the asymptotes. If there is no horizontal or vertical asymptote, enter NA in the associated response area. horizontal NA asymptote: vertical NA asymptote: (c) Give the intervals of increase and decrease of f (I). Note: Use the letter U for union. To enter oo, type infinity with a lower case i. If the function is never increasing or decreasing, enter NAin the associated response area. increasing: NA decreasing: [infinity, infinity)(d) Give the local maximum and minimum values of f (c). Enter your answers in increasing order of the x-value. If there are less than two local extrema, enter NAin the remaining response areas and the corresponding drop-down menu. Include a multiplication sign between symbols. For example, a . IT. )= b whas mexi... )= is a basil mini... (e) Give the intervals of concavity of f (I) . Note: Use the letter U for union. To enter oo, type infinity with a lower case i. If the function is never concave upward or concave downward, enter NA in the associated response area. concave upward: NA concave (infinity, 0) downward:(c) Give the intervals of increase and decrease of f (I). Note: Use the letter U for union. To enter oo, type infinity with a lower case i. If the function is never increasing or decreasing, enter NA in the associated response area. increasing (-infinity, -512) u (0, infinity) decreasir (-512, 0)