The principle of Park Middle School counted all the students in the seventh grade. She found that the ratio of boys to girls was 4:3. There were 42 girls in the seventh grade. How many boys were in the seventh grade?

The perimeter of ? cde is 55 cm. a rhombus dmfn is inscribed in this triangle so that vertices m, f, and n lie on the sides cd , ce , and de respectively. find cd and de if cf=8 cm and ef=12 cm. the answer is not cd=20 and de=15. i have tried that one, it does not work.