How to solve 3x+5y=15

With two variables and one equation there are   "infinite solutions"..

Thus we graph all of them ... see the image for the graph

Step-by-step explanation:

A₁ = 5    an = a₁ + ( n-1) * r
wyliczymy jednak - so we enumerate
a₁ = 5 + (1-1) * (1/6) = 5 + 0* 1/6 = 5 + 0 = 5
a₄ = 5 + (4 - 1) * (1/6) = 5 + 3 * (1/6) = 5 + 3/6 =5 1/2 = 5,5
a₁₀ = 5 + (10 - 1) * (1/6) = 5 + 9 * (1/6)  =  5 + (9/6) = 5 + 3/2 = 6 1/2 = 6,5