Which one is it plsss help

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?

Rose bought a new hat when she was on vacation. the following formula describes the percent sales tax rose paid b=t-c/c

Can someone plz me understand how to do these. plz, show work.in exercises 1-4, rewrite the expression in rational exponent form.[tex]\sqrt[4]{625} \sqrt[3]{512} (\sqrt[5]{4} )³ (\sqrt[4]{15} )^{7}\\ (\sqrt[3]{27} )^{2}[/tex]