[tex] 3(x+1)^{\frac{4}{3}}=48\\\\\frac{3(x+1)^{\frac{4}{3}}}{3}=\frac{48}{3}\\\\(x+1)^{\frac{4}{3}}=(x+1)^{(\frac{1}{3}*4)}=\sqrt[3]{(x+1)^{4}}=16\\\\(\sqrt[3]{(x+1)^{4}})^{3}=16^{3}\\\\(x+1)^4=4096\\\\\sqrt[4]{(x+1)^4}=\sqrt[4]{4096}=\pm8\\\\\\x+1=\pm8\\\\x+1=8\\x=7\\\\x+1=-8\\x=-9[/tex]
Your answers are x = 7 and x = -9.