Any idiot can do simultaneous equations. I think I was about 10 years old when I first came across them.
"I can't do maths" is a euphemism for "I'm too bloody lazy to bother to work something out which requires logical deduction and a set of rules against which to apply the problem".
3x + 7y = 36; 6x - 5y = 15. Calculate the value of (4x + 3y)
(Slide rules and calculators are not permitted.)