The equivalent resistance of n resistors in series is given by:
[tex]R_{eq} = R_1 + R_2 + ... + R_n[/tex]
In our circuit, we have three resistors of [tex]10.0 \Omega[/tex] each, therefore the equivalent resistance of the circuit is
[tex]R_{eq} = R_1 + R_2 + R_3 = 10.0 \Omega + 10.0 \Omega + 10.0 \Omega =30.0 \Omega[/tex]