How to solve simultaneous equations? {a ^ 2 + B ^ 2 = 16 {5 / A ^ 2 + B ^ 2 = 1}

How to solve simultaneous equations? {a ^ 2 + B ^ 2 = 16 {5 / A ^ 2 + B ^ 2 = 1}

① - 2 is a-178; - 5 / a-178; = 15

How to use Mathematica to solve four equations simultaneously?
For example:
Thanks for jcshen's answer^-^
If the equation contains numerical integration, the integration contains E-index, square root and so on, what commands and methods are used to solve these four equations simultaneously?

Similar to the following format, let's see for yourself. I don't think you can use Mathematica symbolic expression. I suggest you borrow books to have a look. There must be examples
Solve[{x*(0.160549*0.21372*(1 - y*Exp[-2z]) - a) == 0.00137,
x*(0.206949*0.21372*(1 - y*Exp[-16z]) - a) == 0.00393,
x*(0.346149*0.21372*(1 - y*Exp[-109z]) - a) == 0.01332,
x*(0.357749*0.21372*(1 - y*Exp[-207z]) - a) == 0.01453},{x,y,z,a}]