Let p=x^2+6p=x 2 +6p, equals, x, start superscript, 2, end superscript, plus, 6. Which equation is equivalent to (x^2+6)^2-21=4x^2+24(x 2 +6) 2 ?21=4x 2 +24left parenthesis, x, start superscript, 2, end superscript, plus, 6, right parenthesis, start superscript, 2, end superscript, minus, 21, equals, 4, x, start superscript, 2, end superscript, plus, 24 in terms of p ?