we use exponential notation; 'the square root of x' is indicated by 'x^(1/2)'

we assume that "and a number...' indicates that 'y cubed' should be added to x raised to the 6th power, but there are many ways to interpret this problem statement!

(x^2 + y^3)^(1/2)

one could also interpret that y^3 is being added to the square root of x^6:

x^(6/2) + y^3