The SSS (side side side) congruence rule says that two triangles are congruent if we have three pairs of sides that are the same length. Any triangle you construct that has side lengths 15, 7, and 5 will be congruent to the original triangle by the SSS rule. You may have to translate, rotate or reflect the second triangle so that it lines up perfectly with the first triangle.
Alternatively, consider triangle ABC that is the given triangle. Let AB = 15, BC = 7, and AC = 5. Then consider another triangle DEF such that DE = 15, EF = 7, and DF = 5. It is possible to do a series of translations, rotations, or reflections such that we get triangle DEF to overlap triangle ABC perfectly.
Since we know he travels at a rate of 1:7.5 all we have to do is divide 7.5 by 30. Do you use proportions? You can set this up as a proportion and the find answer easily.
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Now we cross product.
7.5 multipled by x =7.5x
1x30=30
so now we have
7.5x=30
Now we have to divide 7.5 on both sides which gives us
