Interest from $54,000 @ 10.5% is:

I_1 = 54,000(0.105) = 5,670

Interest from $71,000 @ 4% is:

I_2 = 71,000(0.04) = 2,840

Total Interest is:

I_t = I_1 +I_2 = 5,670 +2,840 = 8,510

If the two principals were loaned as one only, and the Interest is 8,510, then:

I_t = (54,000 +71,000)(r) = 8510

125,000(r) = 8510

r = 8510/125,000 = 0.06808

In percentage,

r = 6.808% --------****

That is the combined interest rate.