so you are going to use the Pythagorean theorem on the smaller triangle to find the connecting side's length

now you can find the bigger triangle's hypotenuse

c=4
2x + 6y = 12
2x - 2x + 6y = 12 - 2x
6y = 12 - 2x
6y/6 = 12/6 - 2x/6
Y = 2 - 2/6 X
Y = 2 - 1/3 X or
Y = -1/3 X + 2.
7/438.... just solve it like thus.....EVERY FRACTION IS A DIVITION PROBLEM