A key word to remember when doing this type of math is "SOHCAHTOA".
Sine =
Opposite over
Hypotenuse
Cosine =
Adjacent over
Hypotenuse
Tangent =
Opposite over
Adjacent
Since this is a 3, 4, 5 triangle, with the sides just multiplied by 7, the opposite of A which is 28 would be simplified to 4.
And the Hypotenuse would be simplified to 5.
So, the answer is 4 / 5!