For simple interest, the equation is
i = prt
interest = (principal/amount deposited) • (rate in decimal form) • (time in years)
To change the 2 1/2% interest to decimal form, first it becomes 2.5% interest, then divide by 100 (moving the decimal place 2 to the left), = 0.025
To calculate interest after 1 year, the equation blanks they gave you left off the time, which is 1, because it won’t change the equation.
0.025 • 250 = $6.25
Interest after 8 years:
i = (250)(0.025)(8)
i = $50
Hope this helps. Let me know in the comments if you have questions, or want to include the rest of the “convince me” section.