Answer:
170 heart beat per minute.
Step-by-step explanation:
While exercising, a person’s recommended target heart rate is a function of age. The recommended number of beats per minute, y, is given by the function y = f(x) = − 0.85x + 187 where x represents a person’s age in years.
So, if my age is 21 years i.e. x = 21, then the number of recommended heart beats per minute for my age will be
y = f(21) = - 0.85(21) + 187 = - 17.85 + 187 = 169.15 ≈ 170. (Answer)
{Taking the larger integer value}
Answer:
20 in
Step-by-step explanation:
Vol. = Bh where B is the area of the base and h is the height of the prism
500 = 25h
h = 20 in

Refer to the attachment for step by step explaination.
The best method for solving the system of linear equation is by the use of algebraic methods.
The system of linear equations can be solved by using the method of simultaneous equations. Here we are given two equations and two unknown variables. We can solve the same by eliminating one of the variables and then either adding or subtracting, find the value of the other variable. Once we know the value of one variable, then we can substitute its value in any one given equation and find the second variable. This method is said to be accurate and does not involve any error.
Hence answer is : USE ALGEBRAIC METHODS
He will earn $427.50 because $4.27 times 90 equals $427.50