## Algebra 1

$15 \space ohm$
Since, the resistances are connected in series combination. Formula to calculate the total resistance, we have $R_{total}=R_1+R_2$ As we are given that $R_1=5 \space ohm$ and $R_{total}=20 \space ohm$ Thus, $20=5+R_2$ $R_2=20-5=15 \space ohm$