a$)$ Create an evenly spaced vector of values from $1$ to $20$ in increments of $1.$ Name your result xa$.$

b$)$ Create a vector of values from $0$ to $2$ in increments of $.$ Name your result xb$.$

c$)$ Create a vector containing $15$ values, evenly spaced between $4$ and $20.$ Use the linspace command. Name your result xc$.$

d$)$ Create a vector containing $10$ values, spaced logarithmically between $10$ and $1000.$ Use the logspace command. Name your result xd$.$