Just enter the formula `ninteg(sin(t)/t, t, 0, x)', type
Z F, and answer the questions. Since this formula contains two
variables, the default argument list will be `(t x)'. We want to
change this to `(x)' since t is really a dummy variable
to be used within ninteg.
The exact keystrokes are Z F s Si RET RET C-b C-b DEL DEL RET y. (The C-b C-b DEL DEL are what fix the argument list.)