I don’t get this can I get help?

The isosceles triangle has two sides of equal length, a, that sre longer than the length of the base ,b. the equation 2a+b=15.7 can be used to find the sides length. if one of the longer sides is 6.3 centimeters what is the length of the base

The angles below are supplementary. what is the value of x? a pair of supplementary angles is shown. one angle measures 7x + 33, and the other angle measures 70. 5.3 8.14 11 14.7

There are 15 plates and each plate is either 7 or 12 inches diameter. which systems of equations do you use to find the number of 7 inch plates, x and 12 inch plates, y