Hi can someone help me plz?

Evaluate the expression for the given value of the variable 7a - 4a for a =8

Given abcd ac=38 and ae=3x+4 find the value of x

Select the correct answer from each drop-down menu. a system of equations and its solution are given below. system a complete the sentences to explain what steps were followed to obtain the system of equations below. system b to get system b, the equation in system a was replaced by the sum of that equation and times the equation. the solution to system b the same as the solution to system a.]