Larger triangle’s base length
a^2 + b^2 = c^2
a^2 + 3^2 = 8^2
a^2 = 8^2 - (3^2)
sqrt(a^2) = sqrt(55)
a = sqrt(55)
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Smaller triangle’s base length:
The same formula applies.
a^2 + 3^2 = 5^2
a^2 = 5^2 - (3^2)
sqrt(a^2) = sqrt(16)
a = 4
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The finale!
Add the two side lengths of a, which is sqrt(55) + 4 (exact answer)
or... 11.416 (unrounded to thousandths place)
Good luck to you!