Find the xvalues of the relative maxima and relative minima

Find the x-value(s) of the relative maxima and relative minima, if any, of the function. (If an answer does not exist, enter DNE.)
f(x)= x^3-75x+4

f(x) = x³ - 75x + 4

f\'(x) = 3x² - 75 = 0

x² = 25

x = ±5

f\'\'(x) = 6x

f\'\'(+5) = +30 > 0

since the graph is concave up, x = +5 is a relative minimum

f\'\'(-5) = -30 < 0

since the graph is concave down, x = -5 is a relative maximum