How to figure the dollar amount that $221.31 is 1,5% of

Hope I have helped you in any way For instance, 25 percent of $1.00 is equal to 25 cents out of a hundred pennies. For 44 percent, it's 44 pennies. The reverse is also true. Fifty-five cents out of 100 pennies is the same as 55 percent.
To calculate percentages based on dollar amounts, such as a 15-percent tip, start by calculating 10 percent. Move the decimal one space to the left to find 10 percent of the total. Then divide that number in half to find what 5 percent is. Add 10 percent and 5 percent to calculate the 15-percent tip.
For example, if the check totals $25.00, move the decimal point one place to the left to find 10 percent, or $2.50. Then halve $2.50 to find 5 percent, or $1.25. Add $2.50 and $1.25 together to get $3.75, which is 15 percent of the check.

7^2 = 6^2 + 9^2 - 2(6)(9)cos(m)
-68 = 2(6)(9)cos(m)
cos(m) = -0.6296
m = arcos ( -0.6296)
m = 129.0 degrees