Solve for y. triangle PQR is congruent to triangle DEF, PQ = 15, QR = 10, RP=8, and EF = 6y + 4

Congruent means that they are identical

looking at the order of the letters in the triangles EF are the last 2 and QR are the last 2

so EF should equal QR

we are told QR = 10 so EF needs to equal 10

so we have 6y+4 = 10

now solve for Y

6y + 4 = 10

subtract 4 from each side:

6y = 6

divide each side by 6

y = 1