"A portfolio is composed of two stocks, A and B$.$ Stock A has a standard deviation of return of $15\%,$ while stock B has a standard deviation of return of $17\%.$ The correlation coefficient between the returns on A and B is $1.$Stock A comprises $75\%$ of the portfolio, while stock B comprises $25\%$ of the portfolio. The standard deviation of the return on this portfolio is $\_\_\_\_\_\_\_\_\_.$ Note: Express your answers in strictly numerical terms. For example, if the answer is $5\%,$ write $0\mathrm{.}05"$