I like trains

V = I · R

If the resistances are in series add them:  R  = R1 + R2

However, if the resistances are in parallel, add their reciprocals:  R  =  1/R1 + 1/R2

So, either:  4.6  =  0.62(2.1 + R2)  

--->         7.419 =  2.1 + R2

--->             5.3  =  R2

or         4.6  =  0.62(1/2.1 + 1/R2)

--->   7.419 =  1/2.1 + 1/R2

--->   6.943  =  1/R2

--->   6.943R2  =  1

--->   R2  =  0.144