When two natural numbers, a and b, are divided, a/b, we can write a=b*q+r where q is the quotient and r the remainder. So a=3b+28 and a or b=43. But the remainder has to be smaller than the divisor, b.
That means a=43*3+28=129+28=157. So we have 157/43=3 remainder 28. The other number is 157.