To find the 4th term of the sequence described by the formula \( a_n = -10(-3)^{n-1} \), we need to substitute \( n = 4 \) into the formula.
Let's calculate \( a_4 \):
\[ a_4 = -10(-3)^{4-1} \] \[ a_4 = -10(-3)^3 \] Now, we calculate \( (-3)^3 \):
\[ (-3)^3 = -27 \]
Next, substitute this back into the equation for \( a_4 \):
\[ a_4 = -10 \cdot (-27) \] \[ a_4 = 270 \]
Thus, the 4th term of the sequence is \( \boxed{270} \).