Now multiply the first number with the $1^{st}$ digit in $2^{nd}$ number to get intermediate results. That is Multiply 15 with 6. Write the result 90 at the end leaving 0 spaces to the right like this.
Now multiply the first number with the $2^{nd}$ digit in $2^{nd}$ number to get intermediate results. That is Multiply 15 with 1. Write the result 15 at the end leaving 1 spaces to the right like this.