What is the current gain of this op-amp circuit?
At \$R_c\$, there is voltage of \$-R_t\cdot I_1\$. Which means that through \$R_c\$ goes current of \$-(\frac{R_t\cdot I_1}{R_c})\$.

So current through \$R_l\$ is sum of currents going through \$R_t\$ and \$R_c\$ and that is \$-I_1-\frac{R_t\cdot I_1}{R_c}\$.

Gain is \$-(1+\frac{R_t}{R_c})\$.