Will give brainiest

evaluate the following expression when a=2 and b=5. show your work.
(2∙a)^(b-1)

evaluate the following expression when a=3 and b= -2. show your work.
〖7a〗^b

what is the order of the mass of electrons from least to greatest?
12.4 x 10-3, 14 x 102, 0.013 x 103, and 157 x 10-4
a. 12.4 x 〖10〗^(-3),14 x 〖10〗^2,0.013 x 〖10〗^3,157 x 〖10〗^(-4)
b. 12.4 x 〖10〗^(-3),157 x 〖10〗^(-4),14 x 〖10〗^2,0.013 x 〖10〗^3
c. 12.4 x 〖10〗^(-3),157 x 〖10〗^(-4),0.013 x 〖10〗^3,14 x 〖10〗^2
d. 0.013 x 〖10〗^3,12.4 x 〖10〗^(-3),157 x 〖10〗^(-4),14 x 〖10〗^2

Arrange the steps to solve this system of linear equations in the correct sequence. x + y = -2 2x – 3y = -9 tiles subtract 3x + 3y = -6 (obtained in step 1) from 2x – 3y = -9 (given) to solve for x. substitute the value of x in the first equation (x + y = -2) to get y = 1. the solution for the system of equations is (-3, 1). x = -15 the solution for the system of equations is (-15, 13). add 3x + 3y = -6 (obtained in step 1) to 2x – 3y = -9 (given), and solve for x. x = -3 substitute the value of x in the first equation (x + y = -2) to get y = 13. multiply the first equation by 3: 3(x + y) = 3(-2) 3x + 3y = -6.