They gave us that these resistors are in parallel, and hence the Total resistance, T, will have the formula of 1/T = 1/R1 + 1/R2. We know that R1=R1 and we know that R2 = R1 + 3. So subbing this in to the formula that they gave us:
1/T = 1/R1 + 1/(R1+3)
Through simplification we can rearrange to get T= (R1^2 + 3R1)/2R1+3. Now sub in R1 = 1 + 1/8 in the equation to find T