Cleo the black lab runs to pick up a stick on the ground at the location x = 3.0 m . the equation of motion for cleo is x = –12.6 m + (5.7 m/s )t.

where is cleo at t = 1.8 s ?

They GAVE you the equation AND the value of the variable.
What more can you ask for ? ! ?

The equation:        x =  -12.6  + 5.7 t

The value of 't':  1.8


The equation:                                 x =  -12.6  + 5.7 t

Write the value in place
of 't' in the equation:                       x =  -12.6  + 5.7 (1.8)

Multiply the 5.7 by the 1.8:              x =  -12.6  + 10.26

Add the  -12.6  and the  10.26 :       x =  -2.34

It makes no difference where the stick is.
That's just extra numbers placed there to distract you.