Solve for S_15
S_{15}=555
Assign S_15
S_{15}≔555
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S_{15}=\frac{15\times 74}{2}
Add 58 and 16 to get 74.
S_{15}=\frac{1110}{2}
Multiply 15 and 74 to get 1110.
S_{15}=555
Divide 1110 by 2 to get 555.
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