Evaluate the definite integrals

a$){\displaystyle \underset{0}{\overset{4}{}}}\sqrt[\phantom{2}]{t}dt=$

b$){\displaystyle \underset{4}{\overset{25}{}}}\frac{1}{\sqrt[\phantom{2}]{z}}dz=$

c$){\displaystyle \underset{8}{\overset{64}{}}}\sqrt[3]{x}dx=$