Plain old cosx has a period of 2π. The variable (t) inside of cos is multiplied by 5, which *compresses* the period. So, the answer is 2π/5

The shift is the quantity subtracted from the variable inside cos. It seems that the shift is divided by the coefficient of t, giving 3π/10. I don't know why this is, but I just varified it with a graphing program and it's true.