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Yes, you can use the formula : D=S*T
For Steve, D1 = S1*T and for Joyce, D2=S2*T
so D1/S1 = D2/S2 ==> S1/D1 = S2/D2 ==> 57/D1 = 63/D2, then you find the 2 numbers that verify that equality (by decomposing 57 and 63) and you can see that 57/19 = 63/21, so D1=19 and the level is 19+11=30.
Regards
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