[MULTIVARIABLE CALCULUS] (10 points) if z = f(x, y) has a continuous second partial derivative and x = s^2 + t^2, y = 3st, find ∂z^2/∂s∂t

Can someone check if i did this right since i really want to make sure it’s correct. if you do you so much

The distribution of the amount of money spent by students for textbooks in a semester is approximately normal in shape with a mean of $235 and a standard deviation of $20. according to the standard deviation rule, how much did almost all (99.7%) of the students spend on textbooks in a semester?

Raymond just got done jumping at super bounce trampoline center. the total cost of his session was $43.25 . he had to pay a $7 entrance fee and $1.25 for every minute he was on the trampoline. write an equation to determine the number of minutes (t) that raymond was on the trampoline.